chore(ci): restrict token permissions (#7470)

Replace read-all with contents:read and add explicit permissions to
follow principle of least privilege.

Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>

.github/workflows/cifuzz.yml

@@ -1,8 +1,13 @@
 name: CIFuzz
+
 on:
   pull_request:
     branches:
       - master
+
+permissions:
+  contents: read
+
 jobs:
   Fuzzing:
     runs-on: ubuntu-latest