[bugfix] Fix create_simple in test environment

api.Request.create_simple has as a positional argument "req_site"
(positional-only would be nice here) but the test implementations
doesn't and requires the parameter as keyword argument.

• Fix create_simple in tests/__init__.py and tests/utils.py
• Fix create_simple in CachedRequest
• Make a keyworded call for Request in api.create_simple
• Update T262926 hint

Bug: T262926
Change-Id: Ie70f83ee1c6cc002177dc0a02b27558915406e7c