[3.11] gh-93453: Only emit deprecation warning in asyncio.get_event_loop when a new event loop is created (#99949)

It no longer emits a deprecation warning if the current event loop was set.

Co-authored-by: Łukasz Langa <lukasz@langa.pl>

Lib/test/test_coroutines.py

@@ -2411,7 +2411,8 @@ class UnawaitedWarningDuringShutdownTest(unittest.TestCase):
     def test_unawaited_warning_during_shutdown(self):
         code = ("import asyncio\n"
                 "async def f(): pass\n"
-                "asyncio.gather(f())\n")
+                "async def t(): asyncio.gather(f())\n"
+                "asyncio.run(t())\n")
         assert_python_ok("-c", code)
 
         code = ("import sys\n"