ci: bump GH Actions to Node 24 runtimes

[Azyyyyyy]

Clears the Node.js 20 is deprecated warning that fires at the top of every job in run 30537101455 and run 30537104274. GitHub started force-shimming Node-20 actions onto Node 24 after the 2025-09-19 deprecation; each action below has a newer major that ships runs.using: node24 natively, so the shim message goes away for good.

Bumps

Every action is bumped to the highest published major that actually flips runs.using: node24, apart from gradle/actions/setup-gradle which is deliberately held at v5 (v6 relicensed the caching component to Gradle's Terms of Use).

Action	From	To	Rationale
actions/checkout	v4	v7	v5 flipped to Node 24; v6 splits creds to a separate file (we don't touch creds); v7 blocks fork-PR checkout for pull_request_target / workflow_run (we don't use those triggers).
actions/setup-java	v4	v5	v5 is the current latest major.
actions/cache	v4	v6	v5 flipped to Node 24; v6 is an ESM refactor with no config change.
actions/upload-artifact	v4	v7	v5 was a false floor + ' — it added preliminary Node 24 support in-code but the action.yml still declared runs.using: node20. v6 flipped the default to node24; v7 adds an opt-in archive: false for single files that we don't use.
actions/download-artifact	v4	v8	Same story: v5/v6 preliminary; v7 flipped the runtime default; v8 is ESM + stricter hash-mismatch defaults + direct-download support. Applies only to name:-keyed downloads (what we use), so the v5 single-artifact-by-ID path fix is inapplicable.
gradle/actions/setup-gradle	v4	v5	v5 is Node 24. v6 intentionally skipped + ' — it moves the caching component into a closed-source gradle-actions-caching library and using it implicitly accepts Gradle's Terms of Use per the v6 blog post.
softprops/action-gh-release	v2	v3	v3 moves runtime to Node 24; v2 is now a Node 20-only line.

Unchanged

• actions/attest-build-provenance@v4 — the v4 line already ships on Node 24.
• reactivecircus/android-emulator-runner@v2 and docker/* — never in the deprecation warning.

Verification

• ✅ Build WASM Docker Image run 30542887308: all three Kotlin jobs green, zero annotations across every check-run (was one per job before).
• 🟡 Mobile Release dry-run run 30542900472 triggered via workflow_dispatch on this branch (publish: false) to confirm the macos-26 iOS job and Android job come out clean too.