Move tox django dependency to proper place

[pcarn]

Description of the Change

In 3451228, I added a tox dependency for django in the wrong place.
Very minor change, just adding it to tox.ini instead.

Checklist

• PR only contains one change (considered splitting up PR)
• unit-test added
• documentation updated
• CHANGELOG.md updated (only for user relevant changes)
• author name in AUTHORS

[n2ygk]

Thanks!

[codecov]

Codecov Report

Merging #1048 (8723fdd) into master (6aeb1b2) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1048   +/-   ##
=======================================
  Coverage   96.64%   96.64%           
=======================================
  Files          31       31           
  Lines        1756     1756           
=======================================
  Hits         1697     1697           
  Misses         59       59           

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