Fix CI by switching to perldocker/perl-tester images

Old perl:5.x Docker images use deprecated manifest v2 schema 1 format
now blocked by GitHub Actions. Switch to perl-actions/perl-versions@v2
for dynamic version discovery and perldocker/perl-tester images.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: miyagawa

.github/workflows/linux.yml

@@ -4,33 +4,30 @@ on:
   - push
 
 jobs:
+  perl-versions:
+    runs-on: ubuntu-latest
+    outputs:
+      perl-versions: ${{ steps.action.outputs.perl-versions }}
+    steps:
+      - id: action
+        uses: perl-actions/perl-versions@v2
+        with:
+          since-perl: 5.14
+
   perl:
+    needs: perl-versions
     runs-on: ubuntu-latest
+    name: "Perl ${{ matrix.perl-version }}"
     strategy:
       fail-fast: false
       matrix:
-        perl-version:
-          - '5.14'
-          - '5.16'
-          - '5.18'
-          - '5.20'
-          - '5.22'
-          - '5.24'
-          - '5.26'
-          - '5.28'
-          - '5.30'
-          - '5.32'
-          - '5.34'
-          - '5.36'
-          - '5.38'
-          - '5.40'
+        perl-version: ${{ fromJson(needs.perl-versions.outputs.perl-versions) }}
     container:
-      image: perl:${{ matrix.perl-version }}
+      image: perldocker/perl-tester:${{ matrix.perl-version }}
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v4
       - name: Install Dependencies
-        run: |
-          curl -sL https://cpanmin.us/ | perl - -nq --with-develop --with-recommends --with-suggests --installdeps .
+        run: cpanm -nq --with-develop --with-recommends --with-suggests --installdeps .
       - name: Run Tests
         run: prove -lr t
         env: