Standardize theme CI gate on the "Required checks pass" aggregator check

The org is moving every repo's branch protection onto one stable required
status check named "Required checks pass", so a repo's ruleset no longer
couples to individual CI job names. The 16 theme repos are subtree mirrors
force-pushed from this monorepo, so their CI gate is defined here, in two
places per theme:

  - .github/workflows/<theme>.yml            (gates this monorepo's PRs)
  - packages/<theme>/.github/workflows/test.yml  (mirrored downstream to
    TryGhost/<Theme>, where branch protection requires the check)

The downstream theme repos' rulesets have already been switched to require
"Required checks pass"; editing the mirror repos directly is futile because the
next subtree force-push overwrites them. Renaming the gate job here — from
all-tests-pass / "All tests pass" to required-checks-pass / "Required checks
pass" across all 32 workflow files — is what actually updates the mirrors when
this merges and republishes, bringing each theme's produced check name back in
line with the check its ruleset now requires.

Pure rename: no job depends on the gate via `needs`, and its failure/cancelled
semantics are unchanged.

Author: aileen

.github/workflows/test.yml

@@ -32,8 +32,8 @@ jobs:
 
       - run: pnpm exec gscan --fatal --verbose .
 
-  all-tests-pass:
-    name: All tests pass
+  required-checks-pass:
+    name: Required checks pass
     if: always()
     needs: [test]
     runs-on: ubuntu-latest