py: Don't use gc or qstr mutex when the GIL is enabled.

There is no need since the GIL already makes gc and qstr operations
atomic.

py/qstr.c

@@ -72,7 +72,7 @@
     #error unimplemented qstr length decoding
 #endif
 
-#if MICROPY_PY_THREAD
+#if MICROPY_PY_THREAD && !MICROPY_PY_THREAD_GIL
 #define QSTR_ENTER() mp_thread_mutex_lock(&MP_STATE_VM(qstr_mutex), 1)
 #define QSTR_EXIT() mp_thread_mutex_unlock(&MP_STATE_VM(qstr_mutex))
 #else