tests/extmod/select_poll_eintr.py: Pre-allocate global variables.

This is a workaround for the case where threading is enabled without a GIL.
In such a configuration, creating a new global variable is not atomic and
threads have race conditions resizing/accessing the global dict.

Signed-off-by: Damien George <damien@micropython.org>

tests/extmod/select_poll_eintr.py

@@ -33,6 +33,14 @@ def thread_main():
     print("thread gc end")
 
 
+# Pre-allocate global variables here so the global dict is not resized by the main
+# thread while the secondary thread runs.  This is a workaround for the bug described
+# in https://github.com/micropython/micropython/pull/11604
+poller = None
+t0 = None
+result = None
+dt_ms = None
+
 # Start a thread to interrupt the main thread during its call to poll.
 lock = _thread.allocate_lock()
 lock.acquire()