Add default_auto_field to BlogAppConfig

[protoroto]

Description

Add default_auto_field to BlogAppConfig to get rid of Django 3.2 warnings

References

Fix #737

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

Patch coverage: 100.00% and no project coverage change.

Comparison is base (bc43947) 94.24% compared to head (14b80ba) 94.24%.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #741   +/-   ##
========================================
  Coverage    94.24%   94.24%           
========================================
  Files           26       26           
  Lines         1823     1824    +1     
  Branches       260      260           
========================================
+ Hits          1718     1719    +1     
  Misses          53       53           
  Partials        52       52           

Flag	Coverage Δ
unittests	94.24% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
djangocms_blog/apps.py	100.00% <100.00%> (ø)

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[coveralls]

coverage: 97.094% (+0.1%) from 96.961% when pulling 14b80ba on protoroto:feature/issue-737-add-default-auto-field into bc43947 on nephila:develop.

[yakky]

👍