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

This is needed in order for packages to be published.

.github/workflows/publish.yaml

diff --git a/.github/workflows/publish.yaml b/.github/workflows/publish.yaml
index 2ec45aa..efc71f6 100644
--- a/.github/workflows/publish.yaml
+++ b/.github/workflows/publish.yaml
@@ -14,3 +14,6 @@
     uses: dart-lang/ecosystem/.github/workflows/publish.yaml@main
     with:
       write-comments: false
+    permissions:
+      id-token: write
+      pull-requests: write