Fix python linting/formatting error when in virtual environment (#4865)

Python fixers and linters were failing when vim is running in a virtual
environment that's located in a path containing text `poetry`. The cause
of this was the regular expression `poetry\|pipenv\|uv$` which matches
`poetry` and `pipenv` if they appear anywhere in the virtualenv path.

ale_linters/python/flake8.vim

@@ -74,7 +74,7 @@ endfunction
 function! ale_linters#python#flake8#GetCommand(buffer, version) abort
     let l:executable = ale_linters#python#flake8#GetExecutable(a:buffer)
 
-    let l:exec_args = l:executable =~? 'pipenv\|poetry\|uv$'
+    let l:exec_args = l:executable =~? '\(pipenv\|poetry\|uv\)$'
     \   ? ' run flake8'
     \   : ''