fix(release): omit redundant setup-node cache selection

Use the established setup-node disable contract: no explicit cache backend and package-manager-cache false. The empty cache value was rejected by the workflow trust guard; retain the guard and add an omission check.

Contract-Neutral: The exact published-RC browser, credential isolation and cache prohibition contract is unchanged; this fixes its setup-node representation.
Change-source: pulse-maintainer

.github/workflows/qualify-browser-update-release.yml

@@ -101,7 +101,6 @@ jobs:
         uses: actions/setup-node@820762786026740c76f36085b0efc47a31fe5020 # v7.0.0
         with:
           node-version: '24.20.0'
-          cache: ''
           package-manager-cache: false
       - name: Prepare Chromium and native tools
         env:

scripts/tests/test_release_lifecycle_rehearsal.py

@@ -183,7 +183,8 @@ class HostedWorkflowCommandFilesTest(unittest.TestCase):
         for field in ('from', 'from_commit', 'to_commit'):
             self.assertIn(f'python3 scripts/write_github_output.py {field} "${field}"', source)
         self.assertNotIn('echo "to_commit=', source)
-        self.assertIn("cache: ''", source)
+        node_setup = source.split('uses: actions/setup-node@', 1)[1].split('      - name:', 1)[0]
+        self.assertNotRegex(node_setup, r'(?m)^\s*cache:')
         self.assertIn('package-manager-cache: false', source)