ci: grant Secret Scanner caller the reusable's job permissions

The standards secret-scanner reusable's gitleaks job declares
pull-requests:write + actions:read (PR summary comment via the Issues/PR
API). A called workflow is capped at the caller's grant, so without these
at the calling job the run dies at startup (0s startup_failure, estate-wide).
Caller-side fix; bumping the pin never fixes it. Ref: hyperpolymath/standards#472.

Author: hyperpolymath

.github/workflows/secret-scanner.yml

@@ -15,6 +15,10 @@ permissions:
 
 jobs:
   scan:
+    permissions:
+      contents: read
+      pull-requests: write
+      actions: read
     uses: hyperpolymath/standards/.github/workflows/secret-scanner-reusable.yml@e9c8888769a703924cc3c0d717900960d78aea00
     secrets: inherit
-    timeout-minutes: 20
+    timeout-minutes: 20