Fix test_write_submit_requires_synced_venv for active-venv resolution

The venv-detection change in condor.py now checks for a giant binary next
to sys.executable before falling back to repo_dir/.venv/bin/giant, and the
test's own pytest venv has one — so the expected FileNotFoundError never
fired. Monkeypatch sys.executable to a nonexistent path so the test exercises
the fallback with neither location populated.

tests/test_condor.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import sys
 from pathlib import Path
 
 import pyarrow.parquet as pq
@@ -223,9 +224,12 @@ def test_write_submit_description(tmp_path: Path):
     assert "--chunk" in body and "--run-dir" in body
 
 
-def test_write_submit_requires_synced_venv(tmp_path: Path):
+def test_write_submit_requires_synced_venv(tmp_path: Path, monkeypatch: pytest.MonkeyPatch):
     run_dir = _prep(_write_inputs(tmp_path))
     cfg = SubmitConfig(run_dir=run_dir, accounting_group="cms", repo_dir=tmp_path)
+    # No `giant` next to the (fake) active interpreter, so this falls through
+    # to repo_dir/.venv/bin/giant, which _write_inputs/_prep also didn't create.
+    monkeypatch.setattr(sys, "executable", str(tmp_path / "not-a-venv" / "bin" / "python"))
     with pytest.raises(FileNotFoundError, match="uv sync"):
         write_submit(cfg)