Fix `passenv` declaration in tox.ini

[rafaelweingartner]

While running the tests locally with the latest tox I was getting the following error message:

pep8: failed with pass_env values cannot contain whitespace, use comma to have multiple values in a single line, invalid values found 'LANG GNOCCHI_TEST_* AWS_*'
  pep8: FAIL code 1 (0.00 seconds)
  evaluation failed :( (0.09 seconds)

That error is happening because of the passenv declaration. This patch is proposing a fix for that.

[rafaelweingartner]

This PR is also going to depend on https://github.com/gnocchixyz/gnocchi/pull/1279

[tobias-urdin]

@mergifyio rebase

[mergify[bot]]

⚠️ This pull request got rebased on behalf of a random user of the organization. This behavior will change on the 1st February 2023, Mergify will pick the author of the pull request instead.

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[mergify[bot]]

rebase

✅ Branch has been successfully rebased

[tobias-urdin]

@mergifyio backport stable/4.4

[mergify[bot]]

backport stable/4.4

✅ Backports have been created

* [#1285 Fix `passenv` declaration in tox.ini (backport #1280)](https://github.com/gnocchixyz/gnocchi/pull/1285) has been created for branch `stable/4.4`