Include to tox a test for requirements*.txt

[kairoaraujo]

small comment: I noticed that there's a space added in the requirements files before the ";" character.
Running pipenv requirements and pipenv requirements --dev-only, with pipenv, version 2022.8.24 I did not get this extra space character.
This currently does not affect anything, but if we add in the future a check in tox to see the diff of the current requirements file and the pipenv requirements command (to know if the requirements are updated), we will get that they are not the same file.

Originally posted by @KAUTH in #80 (comment)