Tune Perl CI workflow

[oalders]

Modernizes .github/workflows/build-and-test.yml via the tune-perl-ci transforms, each landed as its own revertable commit.

Changes

• Disable fail-fast on matrix jobs so one failing Perl/OS cell doesn't mask the rest of the matrix.
• Extend Linux + macOS matrices through Perl 5.42 (adds 5.36/5.38/5.40/5.42 where missing).
• Bump build/coverage containers to perldocker/perl-tester:5.42 (literal-tag images only; matrix-variable tags left alone).
• Add a workflow-level concurrency: block to cancel superseded runs on the same ref.
• Install deps with setup-cpm@v1 + an explicit cpm install run step, replacing the install-with-cpm composite step (drops sudo:, uses version: compat for per-Perl cpm selection).

Not applied

• Restrict push trigger — already conformant (on.push.branches was already ["master"]).
• Drop pre-5.24 macOS/Windows cells — skipped: test-job uses a mixed matrix.os: [ubuntu, macos, windows], where trimming a perl-version entry would also drop the Linux cell. Use an explicit matrix.exclude: block if per-OS trimming is desired.

Also includes the earlier Dependabot config + major-updates bump commits already on this branch.

Each transform's edit was verified with a YAML parse plus a structural assertion before commit.

🤖 Generated with Claude Code

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