tests: pygments 2.14+ highlight whitespace in python code

tests: make sure pygments can detect python script without extension This .t file was failing for me when running run-tests.py with python3.11. Then I tried to run it with python3.10 and it failed anyway, even though it's the default python3 interpreter. But with `python3 ./run-tests.py` it worked fine. And this is what I found while looking at the way pygments lexer checks if a file without extension is likely to be a python script: shebang_matches(text, r'pythonw?(3(\.\d)?)?') Take guess why it doesn't work for python >= 3.10. To work around this issue, we can simply hardcode an "easier" shebang for pygments. This path to python interpreter obviously doesn't need to be accurate, since we're not running this script.

clippy: actually fail if there are any warnings So far, only errors would trip the CI, this makes it so all warnings are elevated to errors, making it a CI fail if any warnings are present. This was the intended behavior, I just missed this when adding clippy.

rust-clippy: fix warning about nested ifs