Update tests for minimum, current Perl version

Minimum "supported" Perl version is 5.20 now, and we should always test
against the latest Perl version too (5.40, at the time of this writing).

Some older Perl images were incompatible with GitHub Actions, so using
release-specific images that are known to work.

.github/workflows/ci.yml

@@ -30,9 +30,9 @@ jobs:
       fail-fast: false
       matrix:
         perl-version:
-          - '5.38'
-          - '5.32'
-          - '5.20'
+          - 'latest'
+          - '5.34-bullseye'
+          - '5.20-buster'
 
     container:
       image: perldocker/perl-tester:${{ matrix.perl-version }}     # https://hub.docker.com/r/perldocker/perl-tester
@@ -63,14 +63,14 @@ jobs:
             dzil test --author --release
 
       - name: Create release
-        if: ${{ matrix.perl-version == '5.38' }}
+        if: ${{ matrix.perl-version == 'latest' }}
         run: |
             # Increase the version number by 0.000001 so in the reports we can be sure we are using the code to be released.
             perl -i -p -e 's/^version\s*=\s*(\d+\.\d+)/"version = " . ($1 + 0.000001)/e' dist.ini
             dzil build
 
       - name: Archive artifacts
-        if: ${{ matrix.perl-version == '5.38' }}
+        if: ${{ matrix.perl-version == 'latest' }}
         uses: actions/upload-artifact@v2
         with:
           name: the-dancer
@@ -86,16 +86,17 @@ jobs:
       fail-fast: false
       matrix:
         perl-version:
-          - '5.38'
-          - "5.32"
-          - "5.14"
+          - 'latest'
+          - "5.34-bullseye"
+          - "5.20-buster"
 #          - "5.28"
 #          - "5.26"
 #          - "5.24"
 #          - "5.22"
-#          - "5.20"
+#- "5.20"
 #          - "5.18"
 #          - "5.16"
+#          - "5.14"
 
     container:
       image: perl:${{ matrix.perl-version }}
@@ -122,7 +123,7 @@ jobs:
       fail-fast: false
       matrix:
         perl-version:
-          - '5.38'
+          - 'latest'
 
     container:
       image: perldocker/perl-tester:${{ matrix.perl-version }}     # https://hub.docker.com/r/perldocker/perl-tester
@@ -166,7 +167,7 @@ jobs:
         # Will resolve and uncomment later.
         #runner: [ubuntu-latest, macos-latest, windows-latest]
         runner: [ubuntu-latest, macos-latest]
-        perl: [ '5.38' ]
+        perl: [ 'latest' ]
 
     runs-on: ${{matrix.runner}}
     name: Native on OS ${{matrix.runner}} Perl ${{matrix.perl}}