ci: fix broken test matrix and update actions

Docker Hub deprecated Image Format v1, breaking pulls for perl:5.8
through perl:5.24 containers on GitHub Actions. This caused all CI
runs (including main branch) to fail on those versions.

- Remove Perl 5.8-5.24 from matrix (Docker images no longer pullable)
- Add Perl 5.34, 5.36, 5.38, 5.40 to matrix
- Update actions/checkout from v2 to v4

The module still supports Perl 5.006+ at runtime; only CI coverage
of versions older than 5.26 is affected by this infrastructure change.

Supersedes #14 and #15.

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

Author: toddr-bot

.github/workflows/testsuite.yml

@@ -19,7 +19,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - run: perl -V
       - name: install dependencies
         uses: perl-actions/install-with-cpm@v1
@@ -46,26 +46,21 @@ jobs:
       matrix:
         perl-version:
           [
+            "5.40",
+            "5.38",
+            "5.36",
+            "5.34",
             "5.32",
             "5.30",
             "5.28",
             "5.26",
-            "5.24",
-            "5.22",
-            "5.20",
-            "5.18",
-            "5.16",
-            "5.14",
-            "5.12",
-            "5.10",
-            "5.8",
           ]
 
     container:
       image: perl:${{ matrix.perl-version }}
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - run: perl -V
       - name: install dependencies
         uses: perl-actions/install-with-cpm@v1
@@ -93,7 +88,7 @@ jobs:
         perl-version: [latest]
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - run: perl -V
       - name: install dependencies
         uses: perl-actions/install-with-cpm@v1