IS0501Test.py: remove trailing slash from /staged endpoint for PATCH

[matthewdicken]

per https://specs.amwa.tv/is-05/releases/v1.1.2/docs/Controllers.html

Controllers performing requests other than GET or HEAD (i.e PUT, POST, DELETE, OPTIONS etc.) MUST use URLs with no trailing slash present.

Currently, test_11_02 and test_12_02 will fail on a node that returns 405: method not allowed for a PATCH on the /staged/ endpoint

[garethsb]

Thanks, @matthewdicken, agree the PATCH request should not have a trailing slash.

The code looks a bit weird with this change, and it also affects the GET request that happens before the PATCH. However, this test suite already has a mix between making GET requests with/without the trailing slash. Generally the GET requests have it and in at least one test case (test_21) the code goes out of the way to issue PATCH without, and GET with. However in one or two places, a GET request is made without the trailing slash.

I say merge this and come back later if we want to consistently test GET requests with/without trailing slash (or both).