ci: give every workflow an explicit least-privilege GITHUB_TOKEN (#13)

CodeQL actions/missing-workflow-permissions: lock.yml, pr-any.yml, push-master.yml had no permissions block, so their jobs received the repository default token. Read-only where nothing writes through GITHUB_TOKEN; lock-threads gets the issues/pull-requests/discussions write it documents; workflows that write do it with a separate bot or app token, so GITHUB_TOKEN stays read-only.

.github/workflows/lock.yml

@@ -5,6 +5,13 @@ on:
   schedule:
     - cron: '15 1/3 * * *'
 
+
+# dessant/lock-threads locks closed issues, PRs and discussions.
+permissions:
+  issues: write
+  pull-requests: write
+  discussions: write
+
 jobs:
   lock:
     runs-on: ubuntu-latest