build-image.yml: Try matrix builds for multiple Perl versions

Try to catch regressions for previous supported Perls more easily by
testing builds ASAP.

.github/workflows/build-image.yml

@@ -1,8 +1,5 @@
 name: Build and test latest supported Perls
 
-env:
-  VERSION: 5.030.003
-
 on: [push, pull_request]
 
 jobs:
@@ -11,6 +8,7 @@ jobs:
     strategy:
       matrix:
         variant: [ 'main', 'slim', 'main,threaded', 'slim,threaded' ]
+        perl-version: [ '5.030.003', '5.028.003' ]
     steps:
       - uses: actions/checkout@master
       - name: Clone docker-library/official-images (for testing)
@@ -19,11 +17,11 @@ jobs:
       - name: Build image
         run: |
           docker version
-          docker build --no-cache -t perl:$VERSION $VERSION-${{ matrix.variant }}-buster
+          docker build --no-cache -t perl:${{ matrix.perl-version }} ${{ matrix.perl-version }}-${{ matrix.variant }}-buster
       - name: Inspect image creation and tag time
         run: |
-          docker image inspect --format \'{{.Created}}\' perl:$VERSION
-          docker image inspect --format \'{{.Metadata.LastTagTime}}\' perl:$VERSION
+          docker image inspect --format \'{{.Created}}\' perl:${{ matrix.perl-version }}
+          docker image inspect --format \'{{.Metadata.LastTagTime}}\' perl:${{ matrix.perl-version }}
       - name: Run tests
         run: |
-          ./official-images/test/run.sh perl:$VERSION
+          ./official-images/test/run.sh perl:${{ matrix.perl-version }}