try fixing typing issues

Author: jorisvandenbossche

pandas/core/arrays/string_arrow.py

@@ -358,17 +358,17 @@ def _is_re_pattern_with_flags(pat: str | re.Pattern) -> bool:
         )
 
     @staticmethod
-    def _preprocess_re_pattern(pat: re.Pattern, case: bool):
+    def _preprocess_re_pattern(pat: re.Pattern, case: bool) -> tuple[str, bool, int]:
+        pattern = pat.pattern
         flags = pat.flags
-        pat = pat.pattern
         # flags is not supported by pyarrow, but `case` is -> extract and remove
         if flags & re.IGNORECASE:
             case = False
             flags = flags & ~re.IGNORECASE
         # when creating a pattern with re.compile and a string, it automatically
         # gets a UNICODE flag, while pyarrow assumes unicode for strings anyway
         flags = flags & ~re.UNICODE
-        return pat, case, flags
+        return pattern, case, flags
 
     def _str_contains(
         self,