build: harden mips64.yml permissions

Signed-off-by: Alex <aleksandrosansan@gmail.com>

.github/workflows/mips64.yml

@@ -2,6 +2,9 @@ name: mips64 qemu test
 
 on: [push, pull_request]
 
+permissions:
+  contents: read # to fetch code (actions/checkout)
+
 jobs:
   TEST:
     runs-on: ubuntu-latest