GH-99205: Mark new interpreters and threads as non-static (GH-99268)

(cherry picked from commit 283ab0e)

Co-authored-by: Brandt Bucher <brandtbucher@microsoft.com>

Author: miss-islington

Diff for: Misc/NEWS.d/next/Core and Builtins/2022-11-08-16-35-25.gh-issue-99205.2YOoFT.rst

@@ -0,0 +1,2 @@
+Fix an issue that prevented :c:type:`PyThreadState` and
+:c:type:`PyInterpreterState` memory from being freed properly.

Diff for: Python/pystate.c

@@ -341,6 +341,7 @@ PyInterpreterState_New(void)
         interp = &runtime->_main_interpreter;
         assert(interp->id == 0);
         assert(interp->next == NULL);
+        assert(interp->_static);
 
         interpreters->main = interp;
     }
@@ -355,6 +356,9 @@ PyInterpreterState_New(void)
         // Set to _PyInterpreterState_INIT.
         memcpy(interp, &initial._main_interpreter,
                sizeof(*interp));
+        // We need to adjust any fields that are different from the initial
+        // interpreter (as defined in _PyInterpreterState_INIT):
+        interp->_static = false;
 
         if (id < 0) {
             /* overflow or Py_Initialize() not called yet! */
@@ -817,6 +821,7 @@ new_threadstate(PyInterpreterState *interp)
         assert(id == 1);
         used_newtstate = 0;
         tstate = &interp->_initial_thread;
+        assert(tstate->_static);
     }
     else {
         // Every valid interpreter must have at least one thread.
@@ -828,6 +833,9 @@ new_threadstate(PyInterpreterState *interp)
         memcpy(tstate,
                &initial._main_interpreter._initial_thread,
                sizeof(*tstate));
+        // We need to adjust any fields that are different from the initial
+        // thread (as defined in _PyThreadState_INIT):
+        tstate->_static = false;
     }
     interp->threads.head = tstate;