ci: restore CODE_SIGNING_* vars for macOS

These were accidentally deleted when shuffling macOS setup steps to an
`macos-setup/action.yml` and back. These variables make Xcode behavior
consistent across different GHA images.

.github/workflows/ci.yml

@@ -100,6 +100,13 @@ jobs:
 
       ### macOS setup
 
+      - name: "macOS: Setup environment"
+        if: runner.os == 'macOS'
+        run: |
+          cat >> $GITHUB_ENV <<EOF
+          CODE_SIGNING_ALLOWED=${{ env.SCRATCH_SHOULD_SIGN }}
+          CODE_SIGNING_REQUIRED=${{ env.SCRATCH_SHOULD_SIGN }}
+          EOF
       - name: "macOS: Setup keys for Fastlane"
         if: runner.os == 'macOS' && env.FASTLANE_ACCESS_KEY != ''
         uses: webfactory/[email protected]