dont need pr read and no fork pr (#48004)

Author: l0lawrence

.github/workflows/typespec-python-regenerate.yml

@@ -20,7 +20,7 @@ on:
 permissions:
   contents: write
   issues: write
-  pull-requests: write
+  pull-requests: read
 
 # Note: with cancel-in-progress, a newer run can cancel an older one after it
 # has force-pushed the branch but before it finishes updating the tracking
@@ -71,6 +71,11 @@ jobs:
             HEAD_SHA=$(echo "$PR_JSON" | jq -r '.headRefOid')
             HEAD_OWNER=$(echo "$PR_JSON" | jq -r '.headRepositoryOwner.login')
             HEAD_REPO_NAME=$(echo "$PR_JSON" | jq -r '.headRepository.name')
+            # Reject fork PRs: head branch must be in microsoft/typespec itself
+            if [ "$HEAD_OWNER/$HEAD_REPO_NAME" != "microsoft/typespec" ]; then
+              echo "::error::Only PRs with head branches in microsoft/typespec are accepted. Fork PRs are not supported (got ${HEAD_OWNER}/${HEAD_REPO_NAME})."
+              exit 1
+            fi
             REPO="${HEAD_OWNER}/${HEAD_REPO_NAME}"
             REF="${HEAD_SHA}"
             DISPLAY_REF="PR #${PR_NUMBER} @ ${HEAD_SHA:0:7}"