Re-enable test_pthread_create_minimal_runtime. NFC (#21719)

Lets see if this flakieness still persists.  I ran the test 10 times
locally and didn't see it.

Author: sbc100

test/test_browser.py

@@ -3875,9 +3875,7 @@ def test_pthread_gcc_spinlock(self):
   @parameterized({
     '': ([],),
     'O3': (['-O3'],),
-    # TODO: re-enable minimal runtime once the flakiness is figured out,
-    # https://github.com/emscripten-core/emscripten/issues/12368
-    # 'minimal_runtime': (['-sMINIMAL_RUNTIME'],),
+    'minimal_runtime': (['-sMINIMAL_RUNTIME'],),
   })
   def test_pthread_create(self, args):
     self.btest_exit('pthread/test_pthread_create.c',