Tests: Prevent shadowing of the Python 3.7 version warning test (#1074)
Tests: Prevent shadowing of the Python 3.7 version warning test (#1074)

Previously the test for Python 3.8 version warnings was named the same
as an earlier test for Python 3.7, meaning the earlier test definition
was overwritten and so never run.

The later test has now been renamed to the correct version, and the
test ordering adjusted for consistency with the rest of the file.

Closes @W-8110123@.

[skip changelog]
Scalingo/python-buildpack,heroku/heroku-buildpack-python,AltSchool/heroku-buildpack-python,AltSchool/heroku-buildpack-python,skilljar/heroku-buildpack-python,Scalingo/python-buildpack,heroku/heroku-buildpack-python