add fix for muting FSTRING_MIDDLE in 3.12+

Author: asottile

pycodestyle.py

@@ -2010,6 +2010,11 @@ def build_tokens_line(self):
                 continue
             if token_type == tokenize.STRING:
                 text = mute_string(text)
+            elif (
+                    sys.version_info >= (3, 12) and
+                    token_type == tokenize.FSTRING_MIDDLE
+            ):
+                text = 'x' * len(text)
             if prev_row:
                 (start_row, start_col) = start
                 if prev_row != start_row:    # different row

testsuite/python36.py

@@ -0,0 +1,2 @@
+#: Okay
+f'{hello}:{world}'