fix_ci

[sergei-iurchenko]

CI was failing for last months because new version of tox (4.0) appeared.
I could not support this version but I fixed old version, deprecated old versions of python, django.
May be somebody will be able to move project to tox 4.0 but it is not target of this PR.

[codecov]

Codecov Report

Merging #512 (4f3ba9a) into master (b6f8e2c) will increase coverage by 6.73%.
The diff coverage is 87.17%.

@@            Coverage Diff             @@
##           master     #512      +/-   ##
==========================================
+ Coverage   83.19%   89.93%   +6.73%     
==========================================
  Files          16       30      +14     
  Lines         601     1023     +422     
  Branches      120      154      +34     
==========================================
+ Hits          500      920     +420     
- Misses         67       68       +1     
- Partials       34       35       +1     

Impacted Files	Coverage Δ
constance/management/commands/constance.py	92.72% <77.77%> (+5.84%)	⬆️
...onstance/migrations/0002_migrate_from_old_table.py	83.33% <83.33%> (ø)
constance/apps.py	100.00% <100.00%> (+5.00%)	⬆️
constance/backends/database.py	58.69% <100.00%> (ø)
constance/migrations/0001_initial.py	100.00% <100.00%> (ø)
constance/models.py	81.25% <100.00%> (ø)
tests/test_admin.py	100.00% <100.00%> (ø)
tests/test_checks.py	100.00% <100.00%> (ø)
tests/test_cli.py	97.77% <100.00%> (ø)

... and 10 files with indirect coverage changes

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[camilonova]

Thank you