fix: avoid races in filesystem ops (#2287)

Use `exist_ok` and `missing_ok` in pathlib operations where we can.

test/test_custom_repair_wheel.py

@@ -21,8 +21,7 @@ platform = wheel.stem.split("-")[-1]
 name = f"spam-0.1.0-py2-none-{platform}.whl"
 dest = dest_dir / name
 dest_dir.mkdir(parents=True, exist_ok=True)
-if dest.exists():
-    dest.unlink()
+dest.unlink(missing_ok=True)
 shutil.copy(wheel, dest)
 """