[3.12] gh-71587: Drop local reference cache to _strptime module in _datetime (gh-120431)

The _strptime module object was cached in a static local variable (in the datetime.strptime() implementation).  That's a problem when it crosses isolation boundaries, such as reinitializing the runtme or between interpreters.  This change fixes the problem by dropping the static variable, instead always relying on the normal sys.modules cache (via PyImport_Import()).

(cherry picked from commit 127c1d2771, AKA gh-120224)

Misc/NEWS.d/next/Library/2024-06-07-11-23-31.gh-issue-71587.IjFajE.rst

@@ -0,0 +1,2 @@
+Fix crash in C version of :meth:`datetime.datetime.strptime` when called again
+on the restarted interpreter.

Modules/_datetimemodule.c

@@ -5209,19 +5209,19 @@ datetime_utcfromtimestamp(PyObject *cls, PyObject *args)
 static PyObject *
 datetime_strptime(PyObject *cls, PyObject *args)
 {
-    static PyObject *module = NULL;
-    PyObject *string, *format;
+    PyObject *string, *format, *result;
 
     if (!PyArg_ParseTuple(args, "UU:strptime", &string, &format))
         return NULL;
 
+    PyObject *module = PyImport_ImportModule("_strptime");
     if (module == NULL) {
-        module = PyImport_ImportModule("_strptime");
-        if (module == NULL)
         return NULL;
     }
-    return PyObject_CallMethodObjArgs(module, &_Py_ID(_strptime_datetime),
+    result = PyObject_CallMethodObjArgs(module, &_Py_ID(_strptime_datetime),
                                         cls, string, format, NULL);
+    Py_DECREF(module);
+    return result;
 }
 
 /* Return new datetime from date/datetime and time arguments. */

Tools/c-analyzer/cpython/globals-to-fix.tsv

@@ -422,7 +422,6 @@ Modules/_ctypes/_ctypes.c	CreateSwappedType	suffix	-
 Modules/_ctypes/_ctypes.c	-	_unpickle	-
 Modules/_ctypes/_ctypes.c	PyCArrayType_from_ctype	cache	-
 Modules/_cursesmodule.c	-	ModDict	-
-Modules/_datetimemodule.c	datetime_strptime	module	-
 Modules/_datetimemodule.c	-	PyDateTime_TimeZone_UTC	-
 Modules/_datetimemodule.c	-	PyDateTime_Epoch	-
 Modules/_datetimemodule.c	-	us_per_ms	-