Update supported Python and Django versions

[yakky]

Description

• Update supported Python and Django versions in tox, github actions and setup.cfg
• Update github actions versions
• Fix missing SECRET_KEY in django-app-helpers settings

References

Fix #135

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 #136 (6d16234) into develop (329a466) will decrease coverage by 1.97%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop     #136      +/-   ##
===========================================
- Coverage   100.00%   98.02%   -1.98%     
===========================================
  Files            5        8       +3     
  Lines          160      456     +296     
  Branches        15       53      +38     
===========================================
+ Hits           160      447     +287     
- Misses           0        6       +6     
- Partials         0        3       +3     

Flag	Coverage Δ
unittests	97.80% <ø> (-1.57%)	⬇️

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Impacted Files	Coverage Δ
meta/__init__.py	100.00% <0.00%> (ø)
meta/models.py	94.04% <0.00%> (ø)
meta/views.py	98.10% <0.00%> (ø)

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