Add nosemgrep to remaining CompletedProcess fixture in test_test_auto_repair

PR #97 Codacy gate failed on issueThreshold (expected 0, got 1): the third
MagicMock(return_value=subprocess.CompletedProcess(...)) fixture (test_truncates_long_diffs,
line 63) was missing the nosemgrep suppression that the other three already had.
No subprocess is actually launched.

Author: JE-Chen

test/unit_test/test_test_auto_repair.py

@@ -60,6 +60,7 @@ def boom(*_a, **_kw):
         self.assertEqual(collect_git_diff("/x", runner=boom), "")
 
     def test_truncates_long_diffs(self):
+        # nosemgrep: dangerous-subprocess-use-audit — fake CompletedProcess for MagicMock; no subprocess is launched.
         fake = MagicMock(return_value=subprocess.CompletedProcess(
             args=[], returncode=0, stdout="x" * 9999, stderr="",
         ))