Upgrade to Django 3.2

[quantum5]

These are the changes required to get the test site to start. We should probably do a far more thorough testing with a database dump import before we deploy this on prod.

[codecov-commenter]

Codecov Report

Base: 46.50% // Head: 46.47% // Decreases project coverage by -0.02% ⚠️

Coverage data is based on head (3abd6c9) compared to base (b676a49).
Patch coverage: 16.66% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1811      +/-   ##
==========================================
- Coverage   46.50%   46.47%   -0.03%     
==========================================
  Files         236      236              
  Lines       13104    13106       +2     
==========================================
- Hits         6094     6091       -3     
- Misses       7010     7015       +5     

Impacted Files	Coverage Δ
dmoj_install_pymysql.py	0.00% <0.00%> (ø)
judge/utils/raw_sql.py	28.98% <0.00%> (-0.87%)	⬇️
judge/widgets/select2.py	56.66% <0.00%> (ø)
judge/admin/profile.py	62.22% <100.00%> (ø)
django_2_2_pymysql_patch.py	42.85% <0.00%> (-42.86%)	⬇️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report at Codecov.
📢 Do you have feedback about the report comment? Let us know in this issue.

[Riolku]

FWIW, the changes look sane, and clicking around on my test site didn't yield anything scary.

I did ~10 minutes of clicking, submitted, event server still works, admin actions seem to work, Celery still works, I ran a batch-rejudge and rescore, tried saving models, didn't see anything strange on Problems or Contests.

[int-y1]

dmoj-wpadmin looks a bit different.

Django 2.2:

Django 3.2:

[Xyene]

LGTM, let's go