fix docs badge link in readme, attempt sphinx theme fix

[FoamyGuy]

This attempts the same fix that was applied in the core from here https://github.com/adafruit/circuitpython/pull/8322/files

While making this change I noticed the badge also linked to a different library so swapped it to this one.

[FoamyGuy]

It turns out that pytest returns an exit code of 5 when "no tests ran" occurs. And it seems to assume tests will follow the naming convention something_test or test_something. Ours was only test before which was causing it not to be found and run, which then led to that exit code 5 which caused the action to fail.

The latest commit renames the file to test_test.py so that it will be found and executed as a test and hopefully allow the actions to pass.

[FoamyGuy]

Merging this to try to validate the RTD fix will work.