Add support for django CMS 3.9

[yakky]

Description

Describe:

• Add support for django CMS 3.9

Django 3.2 still not supported due to plugins lacking support for it

References

Fix #388

Checklist

• I have read the contribution guide
• Code lint checked via inv lint
• changes file included (see docs)
• Usage documentation added in case of new features
• Tests added

[codecov]

Codecov Report

Merging #389 (b60155a) into develop (5f825c0) will decrease coverage by 1.24%.
The diff coverage is 80.00%.

@@             Coverage Diff             @@
##           develop     #389      +/-   ##
===========================================
- Coverage    94.44%   93.20%   -1.25%     
===========================================
  Files            7        9       +2     
  Lines          612      662      +50     
  Branches       128      140      +12     
===========================================
+ Hits           578      617      +39     
- Misses          10       15       +5     
- Partials        24       30       +6     

Flag	Coverage Δ
unittests	93.20% <80.00%> (-1.25%)	⬇️

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Impacted Files	Coverage Δ
djangocms_installer/config/__init__.py	96.29% <72.72%> (-0.92%)	⬇️
djangocms_installer/config/data.py	100.00% <100.00%> (ø)
djangocms_installer/__init__.py	100.00% <0.00%> (ø)
djangocms_installer/main.py	75.00% <0.00%> (ø)

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[coveralls]

Coverage decreased (-0.3%) to 97.734% when pulling b60155a on feature/issue-388-djangocms-39 into 5f825c0 on develop.