Add opt-in GDScript warning for when calling coroutine without await

modules/gdscript/tests/scripts/analyzer/warnings/missing_await.gd

@@ -0,0 +1,7 @@
+func coroutine() -> void:
+	@warning_ignore("redundant_await")
+	await 0
+
+func test():
+	await coroutine()
+	coroutine()