Run integration tests with all supported git versions (#2754)

Run integration tests with various different git versions, more or less
randomly picked from our range of supported versions. Based on
@Ryooooooga's work in #2459, but also restructured a bit.

All tests pass for all git versions, but only after cherry-picking
#2747.

I decided to go with @Ryooooooga's approach and do it without using
docker. I also didn't use docker locally; to reproduce the various
failures that I had to fix, I simply installed the respective git
versions locally and used something like
`PATH=~/git-versions/2.25.1/bin:$PATH
./scripts/run_integration_tests.sh`.

3 files changed, 45 insertions, 9 deletions

diff --git a/.github/workflows/cd.yml b/.github/workflows/cd.yml
index 49fad7731..398fd1ede 100644
--- a/.github/workflows/cd.yml
+++ b/.github/workflows/cd.yml
@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
       - name: Unshallow repo
         run: git fetch --prune --unshallow
       - name: Setup Go
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 3494e6a40..9326ca103 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -28,7 +28,7 @@ jobs:
       GOFLAGS: -mod=vendor
     steps:
       - name: Checkout code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
       - name: Setup Go
         uses: actions/setup-go@v1
         with:
@@ -47,13 +47,47 @@ jobs:
         run: |
           go test ./... -short
   integration-tests:
+    strategy:
+      fail-fast: false
+      matrix:
+        git-version:
+          - 2.20.0 # oldest supported version
+          - 2.22.5
+          - 2.23.0
+          - 2.25.1
+          - 2.30.8
+          - latest # We rely on github to have the latest version installed on their VMs
     runs-on: ubuntu-latest
-    name: "Integration Tests"
+    name: "Integration Tests - git ${{matrix.git-version}}"
     env:
       GOFLAGS: -mod=vendor
     steps:
       - name: Checkout code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
+      - name: Restore Git cache
+        if: matrix.git-version != 'latest'
+        id: cache-git-restore
+        uses: actions/cache/restore@v3
+        with:
+          path: ~/git-${{matrix.git-version}}
+          key: ${{runner.os}}-git-${{matrix.git-version}}
+      - name: Build Git ${{matrix.git-version}}
+        if: steps.cache-git-restore.outputs.cache-hit != 'true' && matrix.git-version != 'latest'
+        run: >
+          sudo apt-get update && sudo apt-get install --no-install-recommends -y build-essential ca-certificates curl gettext libexpat1-dev libssl-dev libz-dev openssl
+          && curl -sL "https://mirrors.edge.kernel.org/pub/software/scm/git/git-${{matrix.git-version}}.tar.xz" -o - | tar xJ -C "$HOME"
+          && cd "$HOME/git-${{matrix.git-version}}"
+          && ./configure
+          && make -j
+      - name: Install Git ${{matrix.git-version}}
+        if: matrix.git-version != 'latest'
+        run: sudo make -C "$HOME/git-${{matrix.git-version}}" -j install
+      - name: Save Git cache
+        if: steps.cache-git-restore.outputs.cache-hit != 'true' && matrix.git-version != 'latest'
+        uses: actions/cache/save@v3
+        with:
+          path: ~/git-${{matrix.git-version}}
+          key: ${{runner.os}}-git-${{matrix.git-version}}
       - name: Setup Go
         uses: actions/setup-go@v1
         with:
@@ -67,9 +101,11 @@ jobs:
           key: ${{runner.os}}-go-${{hashFiles('**/go.sum')}}-test
           restore-keys: |
             ${{runner.os}}-go-
+      - name: Print git version
+        run: git --version
       - name: Test code
         run: |
-          go test pkg/integration/clients/*.go
+          ./scripts/run_integration_tests.sh
   build:
     runs-on: ubuntu-latest
     env:
@@ -77,7 +113,7 @@ jobs:
       GOARCH: amd64
     steps:
       - name: Checkout code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
       - name: Setup Go
         uses: actions/setup-go@v1
         with:
@@ -113,7 +149,7 @@ jobs:
       GOARCH: amd64
     steps:
       - name: Checkout code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
       - name: Setup Go
         uses: actions/setup-go@v1
         with:
@@ -147,7 +183,7 @@ jobs:
       GOFLAGS: -mod=vendor
     steps:
       - name: Checkout code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
       - name: Setup Go
         uses: actions/setup-go@v1
         with:
diff --git a/.github/workflows/sponsors.yml b/.github/workflows/sponsors.yml
index e4c780445..cdf328a73 100644
--- a/.github/workflows/sponsors.yml
+++ b/.github/workflows/sponsors.yml
@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout 🛎️
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
 
       - name: Generate Sponsors 💖
         uses: JamesIves/github-sponsors-readme-action@v1.0.8