checkkeys: Sleeping for 100ms every frame makes the program too unresponsive.

Makes it feel like there's a bug in SDL's text input handling. 10ms is fine.

test/checkkeys.c

@@ -434,7 +434,7 @@ static void loop(void)
     }
 
     /* Slow down framerate */
-    SDL_Delay(100);
+    SDL_Delay(10);
 
 #ifdef SDL_PLATFORM_EMSCRIPTEN
     if (done) {