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

tests/ensure_no_std/Cargo.toml

@@ -2,6 +2,7 @@
 name = "ensure_no_std"
 version = "0.1.0"
 edition = "2021"
+publish = false
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html