Fix PR test workflow for forks

When the workflow is triggered from a fork the permissions for the
`GITHUB_TOKEN` are read-only. This chane skips the write operations if
we're running from a fork.

See: https://docs.github.com/en/actions/reference/events-that-trigger-workflows#pull-request-events-for-forked-repositories

Author: robyoung

.github/workflows/pull-request-test.yml

@@ -20,22 +20,22 @@ jobs:
               issue_number: context.payload.number,
             })
 
-            // Find any comment already made by the bot.
-            const botComment = comments.find(comment => comment.user.id === 41898282)
-            const commentBody = "Hello from actions/github-script! (${{ github.sha }})"
-
-            if (botComment) {
-              await github.issues.updateComment({
-                owner: context.repo.owner,
-                repo: context.repo.repo,
-                comment_id: botComment.id,
-                body: commentBody
-              })
+            if (context.payload.pull_request.head.repo.full_name !== 'actions/github-script') {
+              console.log('Not attempting to write comment on PR from fork');
             } else {
-              await github.issues.createComment({
-                owner: context.repo.owner,
-                repo: context.repo.repo,
-                issue_number: context.payload.number,
-                body: commentBody
-              })
+              if (botComment) {
+                await github.issues.updateComment({
+                  owner: context.repo.owner,
+                  repo: context.repo.repo,
+                  comment_id: botComment.id,
+                  body: commentBody
+                })
+              } else {
+                await github.issues.createComment({
+                  owner: context.repo.owner,
+                  repo: context.repo.repo,
+                  issue_number: context.payload.number,
+                  body: commentBody
+                })
+              }
             }