Add write permission to allow binaries to upload

Uploading binaries to the release requires write permission: this should ensure said permission exists.

.github/workflows/release.yaml

@@ -12,7 +12,7 @@ jobs:
       url: https://pypi.org/p/picamerax
     permissions:
       id-token: write  # IMPORTANT: this permission is mandatory for trusted publishing
-
+      contents: write
     steps:
       - name: Checkout code
         uses: actions/checkout@v2