ci: use supported Go versions

This reduces maintenance burden by letting setup-go track our Go
versions.

actions/setup-go supports "stable" and "oldstable" as automatic aliases
for the latest release and the previous to latest release, which was our
intent with two of these three hard-coded versions.  The third is
hard-coded to match our `go.mod`, which actions/setup-go also supports
reading from, so we can be completely DRY here.

Co-authored-by: Tianon Gravi <[email protected]>
Signed-off-by: Kir Kolyshkin <[email protected]>

Author: kolyshkin

.github/workflows/build.yml

@@ -14,7 +14,10 @@ jobs:
 
     strategy:
       matrix:
-        go: [1.21.x, 1.22.x]
+        # Supported Go releases plus the version in the go.mod are tested. See:
+        #  - https://github.com/actions/setup-go/tree/v5#getting-go-version-from-the-gomod-file
+        #  - https://github.com/actions/setup-go/tree/v5#using-stableoldstable-aliases
+        go: ['go.mod', 'oldstable', 'stable']
 
     steps:
       - name: checkout source code
@@ -23,7 +26,8 @@ jobs:
       - name: setup go environment
         uses: actions/setup-go@v5
         with:
-          go-version: ${{ matrix.go }}
+          go-version: ${{ matrix.go != 'go.mod' && matrix.go || null }}
+          go-version-file: ${{ matrix.go == 'go.mod' && 'go/src/github.com/opencontainers/image-spec/go.mod' || null }}
 
       - name: create go.mod
         run: |