Auto trigger PR reviews when they are from branches in repo (#234)

Pull request events identify members as "contributors", so the workflows
are not auto-triggered. But there are some contributors who are not
members, so workflows would fail on forks.

In this change, we switch the condition for PR events to check for
whether the PR was created from a branch in the repo or from a fork.

Note that only users with write access to the repo can create branches.

Fixes #175

cc @leehagoodjames @sethvargo

Author: jerop

.github/workflows/gemini-dispatch.yml

@@ -43,10 +43,13 @@ jobs:
           env | grep '^DEBUG_'
 
   dispatch:
+    # For PRs: only if not from a fork
+    # For comments: only if user types @gemini-cli and is OWNER/MEMBER/COLLABORATOR
+    # For issues: only on open/reopen
     if: |-
       (
         github.event_name == 'pull_request' &&
-        contains(fromJSON('["OWNER", "MEMBER", "COLLABORATOR"]'), github.event.pull_request.author_association)
+        github.event.pull_request.head.repo.fork == false
       ) || (
         github.event.sender.type == 'User' &&
         startsWith(github.event.comment.body || github.event.review.body || github.event.issue.body, '@gemini-cli') &&