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

@@ -12,5 +12,9 @@ permissions:
   contents: read
 jobs:
   scan:
+    permissions:
+      contents: read
+      pull-requests: write
+      actions: read
     uses: hyperpolymath/standards/.github/workflows/secret-scanner-reusable.yml@d135b05bfc647d0c0fbfedc7e80f37ea50f49236
-    secrets: inherit
+    secrets: inherit