Add pull request and id-token write permissions to publish.yaml (#351)

This is needed in order for packages to be published.

Author: srujzs

.github/workflows/publish.yaml

@@ -14,3 +14,6 @@ jobs:
     uses: dart-lang/ecosystem/.github/workflows/publish.yaml@main
     with:
       write-comments: false
+    permissions:
+      id-token: write
+      pull-requests: write