chore: skip CI checks on the release PR (DEV-6678)

[mpro7]

DEV-6678

Summary

• Release PRs (head branch release-please--*) only bump CHANGELOG.md and version.txt — no source changes — yet they currently run the full build-and-test.yml suite (unit, IT, E2E, bagit/jwt/shacl, ingest-IT, docs, formatting, fuseki-version, healthcheck). This wastes CI resources and delays the release PR going green.
• Every job in build-and-test.yml is now gated on !startsWith(github.head_ref, 'release-please'), so all of them skip on the release PR. This mirrors the approach already in use in dsp-app.

Changes

• .github/workflows/build-and-test.yml:
  • Jobs that ran on both push and PR (build-and-test, test-it, test-e2e) gain if: ${{ !startsWith(github.head_ref, 'release-please') }}.
  • PR-gated jobs (test-bagit, test-jwt, test-shacl-validator, test-ingest-integration, test-docs-build, check-fuseki-version-consistency, check-formatting, docker-healthcheck) get the same clause appended to their existing github.event_name == 'pull_request' condition.
  • upload-coverage needs the skipped jobs, so it skips automatically — no change.
  • Added a comment block explaining the rationale and the branch-protection semantics.

Why this is safe

• Normal PRs: head_ref is the feature branch → full suite runs (unchanged).
• Push to main: head_ref is empty → !startsWith('', 'release-please') is true → build-and-test/test-it/test-e2e still run, preserving the per-main-commit Codecov baseline; PR-gated jobs stay off via github.event_name. The post-merge release-commit run is intentionally not skipped.
• Release PR: all jobs skip. A required status check skipped via a job-level if: is reported as skipped, which branch protection counts as passing — so the release PR stays mergeable. The whole workflow still triggers (no on:-level filtering), avoiding the "never reported → blocks merge" footgun.
• Scope is build-and-test.yml only; the separate Check PR Title workflow is left running (the release title matches its regex; sub-second cost).

Test Plan

• actionlint passes on the change (only a pre-existing warning about the custom ubuntu-latest-large-runner label, unrelated to this PR).
• YAML parses; inline # gate-only comments do not bleed into the if: expressions.
• The expression form !startsWith(github.head_ref, 'release-please') is already used in dsp-app's codeql-analysis.yml and cloud-run-pr-preview.yml, and dsp-app's gated jobs are themselves required checks — first-party confirmation that skipped-required-via-if passes branch protection in this org.
• No local unit test is possible for GitHub Actions skip semantics; final confirmation is observational on the next release PR (checks show as skipped and the PR is mergeable).

🤖 Generated with Claude Code

[linear-code]

DEV-6678

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.98%. Comparing base (a978c50) to head (aba8cca).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4162   +/-   ##
=======================================
  Coverage   85.98%   85.98%           
=======================================
  Files         538      538           
  Lines       30571    30571           
  Branches     3559     3559           
=======================================
  Hits        26286    26286           
  Misses       4285     4285           

Flag	Coverage Δ
e2e	85.98% <ø> (ø)
integration	85.98% <ø> (ø)
unit	85.98% <ø> (ø)

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