Rename MYPY as TYPE_CHECKING (see python/mypy#18443)

Author: hukkin

src/tomli/_parser.py

@@ -16,8 +16,8 @@
     match_to_number,
 )
 
-MYPY = False
-if MYPY:  # pragma: no cover
+TYPE_CHECKING = False
+if TYPE_CHECKING:
     from collections.abc import Iterable
     from typing import IO, Any, Final
 

src/tomli/_re.py

@@ -8,8 +8,8 @@
 from functools import lru_cache
 import re
 
-MYPY = False
-if MYPY:  # pragma: no cover
+TYPE_CHECKING = False
+if TYPE_CHECKING:
     from typing import Any, Final
 
     from ._types import ParseFloat