fix(ci): upgrade actions/cache to v5 and fix container git checkout

[317787106]

What does this PR do?

• Upgrades actions/cache from v4 to v5 in pr-build.yml, pr-check.yml, and system-test.yml (7 occurrences) to resolve the Node.js 20 deprecation warning on GitHub Actions runners.
• Reorders the container-based jobs in pr-build.yml (docker-build-rockylinux, docker-build-debian11, coverage-base) so the dependency-install step runs before actions/checkout. This ensures git (and the other build tools) are on the PATH at checkout time, so the action performs a real git clone instead of falling back to the GitHub REST API.

Why are these changes required?

• GitHub is deprecating Node.js 20 on Actions runners: actions still on Node.js 20 will be forced to Node.js 24 by default starting June 16, 2026, and Node.js 20 will be removed entirely on September 16, 2026. actions/cache@v4 uses Node.js 20; upgrading to v5 moves it to Node.js 24 and eliminates the deprecation warning.
• The container base images (rockylinux:8, eclipse-temurin:8-jdk) ship without git. Because the install step previously ran after actions/checkout, the action could not find git on the PATH and emitted the warning "The repository will be downloaded using the GitHub REST API / To create a local Git repository instead, add Git 2.18 or higher to the PATH", checking out the source without a .git directory. Installing the dependencies first removes the warning and yields a proper local Git repository.

This PR has been tested by:

• CI workflow validation

Follow up

Re-enable build-ubuntu once ubuntu-24.04-arm runner stability is confirmed.

[bladehan1]

Automated review by AI pipeline (see .review-system/tasks/PR6808 for full artifacts).

Decision: Approve
Findings: P0=0, P1=0, P2=1, nit=1

NOTE: This review was generated by Claude Code's /review pipeline. Comments are AI suggestions; human reviewers retain final judgment.

[bladehan1]

[NIT] build-ubuntu disable strategy — 2 small follow-ups

Both items relate to the commented-out build-ubuntu job:

1. "deprecate" vs "temporarily disable" in PR title/commit. The PR title says "deprecate ubuntu 24 + aarch64", but the description says "re-enable once the runner stabilizes" — these are contradictory. "Deprecate" implies a planned phase-out with a notice period; what's happening here is a temporary workaround for an upstream runner instability. The PR title will land in git log and any generated changelog. Consider amending the commit subject to something like: fix(ci): update action cache to v5; temporarily disable ubuntu-24.04-arm build

2. No tracking reference in the comment block. The commented-out job has no link back to the upstream issue that caused the disable. Without it, there's no automated way to discover this when the runner stabilises. Consider adding a line above the block:

   # TODO: Re-enable once actions/runner-images#14100 is resolved

Suggestion: Amend the commit/PR title to say "temporarily disable" instead of "deprecate", and add a TODO comment with the upstream issue reference above the commented block.

[317787106]

ubuntu-24.04-arm appears to have become available today, so it is likely to continue working.

[317787106]

ubuntu-24.04-arm has been uncomment and keep it stay.