Fix C&P error in test_toy_cuda_sanity_check and simplify

[Flamefire]

The major issue was in assert_cuda_report which wrongly was calling assert_regex(num_checked_str, outtxt, stdout).
But the parameter to the function is log not outtxt

This went undetected because we do not enable the Flake8 check for unused variables/parameters.
I'd argue we should, even if that means a bit initial refactoring: Most uses should be ok, so we simply silence the warning by using _ as the name or prefix the variable with an underscore.

While doing that I noticed that there are a lot of assertTrue checks when testing for a regex. In #5137 I replaced many of those already by the better assertRegex which avoids us having to specify the message.
This removes almost half of the lines of the test: 1. Compile regex, 2. Assemble message, 3. do the check are replaced by just doing the check.

There were also cases where the regex was wrong, e.g. r"Missing compute capabilities: 8.0."
The dot would need to be escaped, but the better check is assertIn, we don't need a regex here.