Silence experimental coroutine deprecation warnings (GH-150788)

(cherry picked from commit 7241db1)

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>
Co-authored-by: Zachary Ware <zach@python.org>

Author: 2 people

PC/python_uwp.cpp

@@ -13,6 +13,7 @@
 #if defined(__clang__)
 #define _SILENCE_CLANG_COROUTINE_MESSAGE
 #endif
+#define _SILENCE_EXPERIMENTAL_COROUTINE_DEPRECATION_WARNINGS
 
 #include <appmodel.h>
 #include <winrt\Windows.ApplicationModel.h>