[3.15] gh-143008: Fix race re-initializing TextIOWrapper (#151203)

__init__() changes multiple variables and may be called more than once
from multiple threads.

(cherry picked from commit 0318867)

Author: cmaloney

Misc/NEWS.d/next/Library/2026-06-04-18-22-56.gh-issue-143008.z5tw-J.rst

@@ -0,0 +1 @@
+Fix race conditions when re-initializing a :class:`io.TextIOWrapper` object.

Modules/_io/clinic/textio.c.h

@@ -1049,6 +1049,7 @@ io_check_errors(PyObject *errors)
 
 
 /*[clinic input]
+@critical_section
 _io.TextIOWrapper.__init__
     buffer: object
     encoding: str(accept={str, NoneType}) = None
@@ -1092,7 +1093,7 @@ _io_TextIOWrapper___init___impl(textio *self, PyObject *buffer,
                                 const char *encoding, PyObject *errors,
                                 const char *newline, int line_buffering,
                                 int write_through)
-/*[clinic end generated code: output=72267c0c01032ed2 input=e6cfaaaf6059d4f5]*/
+/*[clinic end generated code: output=72267c0c01032ed2 input=0f077220214c40a4]*/
 {
     PyObject *raw, *codec_info = NULL;
     PyObject *res;