ci: mark failed macOS builds as neutral instead of failure

Use the Checks API to flip failed macOS build conclusions to neutral
(gray dash) so unstable builds don't show red X marks on PRs.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/build-tests-mac.yml

@@ -8,6 +8,9 @@ concurrency:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
   cancel-in-progress: true
 
+permissions:
+  checks: write
+
 jobs:
   buildForAllPlatformsMacOS:
     name: ${{ matrix.targetPlatform }} on ${{ matrix.unityVersion }}
@@ -86,3 +89,35 @@ jobs:
           name: Build ${{ matrix.targetPlatform }} on MacOS (${{ matrix.unityVersion }})${{ matrix.buildProfile && '  With Build Profile' || '' }}
           path: build
           retention-days: 14
+
+  markUnstableBuilds:
+    name: Mark unstable macOS builds
+    needs: buildForAllPlatformsMacOS
+    if: always()
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/github-script@v7
+        with:
+          script: |
+            const { data: checkRuns } = await github.rest.checks.listForRef({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              ref: context.sha,
+              per_page: 100,
+            });
+
+            for (const run of checkRuns.check_runs) {
+              if (run.conclusion !== 'failure' || run.app?.slug !== 'github-actions') continue;
+              if (!run.name.includes('StandaloneOSX') && !run.name.includes('iOS')) continue;
+
+              await github.rest.checks.update({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                check_run_id: run.id,
+                conclusion: 'neutral',
+                output: {
+                  title: `${run.name} (unstable)`,
+                  summary: 'This macOS build is unstable and its failure does not block merging.',
+                },
+              });
+            }