fix: correct assignee trigger test to handle different assignee properly (#178)

* fix: use direct assignee field

* fix: correct assignee trigger test to handle different assignee properly

The test was failing because the mockIssueAssignedContext was missing the
top-level assignee field that the trigger validation logic checks. Added
the missing assignee field to the mock context and updated the test to
properly override both the top-level assignee and issue.assignee fields
when testing assignment to a different user.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* Adjust IssuesAssignedEvent import position (#2)

---------

Co-authored-by: Claude <noreply@anthropic.com>

src/github/context.ts

@@ -1,6 +1,7 @@
 import * as github from "@actions/github";
 import type {
   IssuesEvent,
+  IssuesAssignedEvent,
   IssueCommentEvent,
   PullRequestEvent,
   PullRequestReviewEvent,
@@ -147,3 +148,9 @@ export function isPullRequestReviewCommentEvent(
 ): context is ParsedGitHubContext & { payload: PullRequestReviewCommentEvent } {
   return context.eventName === "pull_request_review_comment";
 }
+
+export function isIssuesAssignedEvent(
+  context: ParsedGitHubContext,
+): context is ParsedGitHubContext & { payload: IssuesAssignedEvent } {
+  return isIssuesEvent(context) && context.eventAction === "assigned";
+}