fix(ci): check out API-created dep branch via remote-tracking ref

git fetch origin <branch> only sets FETCH_HEAD, so the silent checkout
failure left commits on the wrong ref and the push failed. Fetch into
refs/remotes/origin/<branch> and checkout -B from it.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

tests/unit/test_create_dependency_pr.py

@@ -557,3 +557,27 @@ class TestBranchCreation:
         result = self._invoke()
         assert result.exit_code != 0
         assert "Failed to create branch" in result.output
+
+    @patch("devx.ci.create_dependency_pr.create_vikunja_task", return_value=None)
+    @patch("devx.ci.create_dependency_pr.update_manifest", return_value=True)
+    @patch("devx.ci.create_dependency_pr.read_manifest_version", return_value="0.9.0")
+    @patch("devx.ci.create_dependency_pr.find_existing_pr", return_value=None)
+    @patch("devx.ci.create_dependency_pr.GiteaClient")
+    @patch("devx.ci.create_dependency_pr.get_ci_token", return_value="tok")
+    def test_checks_out_remote_tracking_branch(
+        self,
+        _token: MagicMock,
+        mock_client_cls: MagicMock,
+        _find: MagicMock,
+        _read: MagicMock,
+        _update: MagicMock,
+        _task: MagicMock,
+    ) -> None:
+        import subprocess
+
+        self._client(mock_client_cls)
+        result = self._invoke()
+        assert result.exit_code == 0
+        calls = [c.args[0] for c in subprocess.run.call_args_list]
+        assert ["git", "fetch", "origin", "deps/sso_bridge-0.9.1:refs/remotes/origin/deps/sso_bridge-0.9.1"] in calls
+        assert ["git", "checkout", "-B", "deps/sso_bridge-0.9.1", "origin/deps/sso_bridge-0.9.1"] in calls