Fix type annotations (#13358)

* Fix type annotations

* fix: update the syntax to use | 

the type hint str | (str, int) is not the correct syntax for defining a union type that includes a tuple.

* Use typing module for annotations instead (for python version <3.10)

---------

Co-authored-by: Jennifer Davis <sigje@google.com>

Author: GameRoMan

trace/cloud-trace-demo-app-opentelemetry/app/app.py

@@ -20,6 +20,8 @@
 import random
 import time
 
+from typing import Tuple, Union
+
 import flask
 
 # [START trace_demo_imports]
@@ -62,7 +64,7 @@ def configure_exporter(exporter):
 
 
 @app.route("/")
-def template_test() -> str or (str, int):
+def template_test() -> Union[str, Tuple[str, int]]:
     # Sleep for a random time to imitate a random processing time
     time.sleep(random.uniform(0, 0.5))