Update Django 4.0 version in tox.ini to RC1

[pauloxnet]

No description provided.

[codecov]

Codecov Report

Merging #1531 (666cc22) into main (f5454d7) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1531   +/-   ##
=======================================
  Coverage   85.87%   85.87%           
=======================================
  Files          35       35           
  Lines        1883     1883           
  Branches      274      274           
=======================================
  Hits         1617     1617           
  Misses        187      187           
  Partials       79       79           

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[matthiask]

Thanks!