[#3689] Fix filesystem searcher and tests that mock it (#4271)

automatic commit by git-black, original commits:
  3d28b67
  d246bab

core/dbt/parser/search.py

@@ -67,9 +67,7 @@ def filesystem_search(project: Project, relative_dirs: List[str], extension: str
     file_path_list = []
     for result in find_matching(root, relative_dirs, ext):
         if "searched_path" not in result or "relative_path" not in result:
-            raise InternalException(
-                'Invalid result from find_matching: {}'.format(result)
-            )
+            raise InternalException("Invalid result from find_matching: {}".format(result))
         file_match = FilePath(
             searched_path=result["searched_path"],
             relative_path=result["relative_path"],