user32/tests: Free window after use.

dlls/user32/tests/class.c

diff --git a/dlls/user32/tests/class.c b/dlls/user32/tests/class.c
index 940550e..b11b5d2 100644
--- a/dlls/user32/tests/class.c
+++ b/dlls/user32/tests/class.c
@@ -572,6 +572,7 @@
     SetClassLongPtrA( hwnd, GCLP_HMODULE, 0xdeadbeef );
     check_instance( "EDIT", (HINSTANCE)0x12345678, (HINSTANCE)0x12345678, (HINSTANCE)0xdeadbeef );
     check_thread_instance( "EDIT", (HINSTANCE)0x12345678, (HINSTANCE)0x12345678, (HINSTANCE)0xdeadbeef );
+    DestroyWindow(hwnd);
 }
 
 static void test_builtinproc(void)