Update sphinx_autobuild/filter.py

Author: AA-Turner

sphinx_autobuild/filter.py

@@ -24,7 +24,7 @@ def __repr__(self):
     def __call__(self, filename: str, /):
         """Determine if 'path' should be ignored."""
         normalised_path = Path(filename).resolve().as_posix()
-        if os.getenv("SPHINX_AUTOBUILD_DEBUG") not in (None, "", "0"):
+        if os.getenv("SPHINX_AUTOBUILD_DEBUG") not in {None, "", "0"}:
             print(
                 f"SPHINX_AUTOBUILD_DEBUG: {normalised_path!r} has changed; "
                 f"ignores are {self}"