Update release-plz GitHub workflow (#466)

- Disable publishing for `ensure_no_std` test crate
- Add write content permissions to release-plz job expliclity

Signed-off-by: Burak Varlı <burakvar@amazon.co.uk>

.github/workflows/release-plz.yml

@@ -10,6 +10,8 @@ jobs:
   release-plz:
     name: Release-plz
     runs-on: ubuntu-latest
+    permissions:
+      contents: write
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4