CI: run tests separately from build jobs

Reorganize GitHub Actions workflows to run tests the same way on all Go
versions, and so remove running tests from the 'build' jobs (which run
job only on 'oldstable' and 'stable').

This makes the build matrix of the 'test' job more consistent.

Add comments explaining the logic of each build matrix.

Author: dolmen

.github/workflows/main.yml

@@ -7,6 +7,8 @@ jobs:
     strategy:
       matrix:
         go_version:
+          # Our developer environment (especially the code generator)
+          # must work with all the supported Go releases.
           - stable
           - oldstable
     steps:
@@ -18,13 +20,19 @@ jobs:
       - run: ./.ci.gogenerate.sh
       - run: ./.ci.gofmt.sh
       - run: ./.ci.govet.sh
-      - run: go test -v -race ./...
 
-  test-old-go:
+  test:
     runs-on: ubuntu-latest
     strategy:
       matrix:
         go_version:
+          # Tested version are ordered for faster useful feedback:
+          # 'stable' and 'oldstable' are the most important
+          # then the oldest supported version from go.mod
+          # then the other intermediary Go versions (which, at this point
+          # have low chance to fail if the other succeeded)
+          - stable
+          - oldstable
           - "1.17"
           - "1.18"
           - "1.19"
@@ -39,7 +47,8 @@ jobs:
         uses: actions/setup-go@4a3601121dd01d1626a1e23e37211e3254c1c06c # v6.4.0
         with:
           go-version: ${{ matrix.go_version }}
-      - run: go test -v -race ./...
+      - name: Test
+        run: go test -v -race ./...
 
   check-actions-hashes:
     runs-on: ubuntu-latest