fix: add missing import and update tests for branch template feature (#799)

* fix: add missing import and update tests for branch template feature

- Add missing `import { $ } from 'bun'` in branch.ts
- Add missing `labels` property to pull-request-target.test.ts fixture
- Update branch-template tests to expect 5-word descriptions

* address review feedback: update comment and add truncation test

src/github/operations/branch.ts

@@ -6,6 +6,7 @@
  * - For Issues: Create a new branch
  */
 
+import { $ } from "bun";
 import { execFileSync } from "child_process";
 import * as core from "@actions/core";
 import type { ParsedGitHubContext } from "../context";