Run tests on a matrix of go versions (golang#168)

Resolves golang#163

Author: panmari

.github/workflows/go.yml

@@ -16,16 +16,18 @@ jobs:
 
   build:
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        # Test on supported go compiler releases as well as the oldest version we support from go.mod.
+        go: [ '1.21.0', 'oldstable', 'stable' ]
+    name: Go version ${{ matrix.go }}
     steps:
     - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
 
     - name: Set up Go
       uses: actions/setup-go@0aaccfd150d50ccaeb58ebd88d36e91967a5f35b # v5.4.0
       with:
-        # TODO: enable [matrix testing](https://github.com/marketplace/actions/setup-go-environment#matrix-testing)
-        # so that we can test on both stable, oldstable and the oldest version
-        # we currently support (as specified in go.mod).
-        go-version: 'stable'
+        go-version: ${{ matrix.go }}
 
     - name: Build
       run: go build -v ./...