ci: reduce pull request build matrices

[ousamabenyounes]

Fixes #2580.

What changed

• Added .github/scripts/ci-build-matrix.sh to centralize Docker/static build matrix selection.
• Pull requests without the full-build-matrix label now run a reduced build matrix:
  • Docker images: one bookworm variant per PHP version on linux/amd64.
  • Static binaries: linux/amd64 only.
• Pushes, schedules, releases, manual runs, and PRs labeled full-build-matrix keep the full matrix.

RED

.github/scripts/ci-build-matrix-test.sh

.github/scripts/ci-build-matrix-test.sh: line 12: .github/scripts/ci-build-matrix.sh: No such file or directory

GREEN

.github/scripts/ci-build-matrix-test.sh
bash -n .github/scripts/ci-build-matrix.sh .github/scripts/ci-build-matrix-test.sh
docker run --rm --label com.ora.cleanup.scope=contribute -v "$PWD":/work -w /work mikefarah/yq:4.47.2 '.name' .github/workflows/docker.yaml .github/workflows/static.yaml\n\nBuild Docker Images\n---\nBuild binary releases\n```\n\n## Matrix smoke checks\n```\nMETADATA="$(docker buildx bake --print | jq -c)" .github/scripts/ci-build-matrix.sh docker false\nvariants=["php-8-2-bookworm","php-8-3-bookworm","php-8-4-bookworm","php-8-5-bookworm"]\nplatforms=["linux/amd64"]\n\nMETADATA="$(docker buildx bake --print static-builder-musl | jq -c)" .github/scripts/ci-build-matrix.sh static false\nplatforms=["linux/amd64"]\n```