Disable GC even during finalizing

We're seeing a crash during shutdown in rb_gc_impl_objspace_free because
it's running lazy sweeping during shutdown. It appears that it's due to
`finalizing` being set, which causes GC to not be aborted and not
disabled which causes it to be in lazy sweeping at shutdown.

The full stack trace is:

    #6  rb_bug (fmt=fmt@entry=0x5643b8ebde78 "lazy sweeping underway when freeing object space") at error.c:1095
    #7  0x00005643b8a3c697 in rb_gc_impl_objspace_free (objspace_ptr=<optimized out>) at gc/default.c:9507
    #8  0x00005643b8c269eb in ruby_vm_destruct (vm=0x7e2fdc84d000) at vm.c:3141
    #9  0x00005643b8a5147b in rb_ec_cleanup (ec=<optimized out>, ex=<optimized out>) at eval.c:263
    #10 0x00005643b8a51c93 in ruby_run_node (n=<optimized out>) at eval.c:319
    #11 0x00005643b8a4c7c7 in rb_main (argv=0x7fffef15e7f8, argc=18) at ./main.c:43
    #12 main (argc=<optimized out>, argv=<optimized out>) at ./main.c:62

gc/default.c

@@ -3233,11 +3233,17 @@ rb_gc_impl_shutdown_call_finalizer(void *objspace_ptr)
 #if RGENGC_CHECK_MODE >= 2
     gc_verify_internal_consistency(objspace);
 #endif
-    if (RUBY_ATOMIC_EXCHANGE(finalizing, 1)) return;
 
     /* prohibit incremental GC */
     objspace->flags.dont_incremental = 1;
 
+    if (RUBY_ATOMIC_EXCHANGE(finalizing, 1)) {
+        /* Abort incremental marking and lazy sweeping to speed up shutdown. */
+        gc_abort(objspace);
+        dont_gc_on();
+        return;
+    }
+
     /* force to run finalizer */
     while (finalizer_table->num_entries) {
         struct force_finalize_list *list = 0;