Mypy 1.7.1

[dantownsend]

When upgrading to the latest Mypy and Pylance, quite a few type errors were reported.

This PR fixes any type errors reported by the latest MyPy.

There should be overlap with Pylance (which seems even stricter than Mypy now), but will fix those in a separate PR.

[codecov-commenter]

Codecov Report

Attention: 14 lines in your changes are missing coverage. Please review.

Comparison is base (5f972d0) 92.09% compared to head (355208f) 92.03%.

Files	Patch %	Lines
piccolo/apps/migrations/auto/schema_differ.py	16.66%	5 Missing ⚠️
piccolo/apps/schema/commands/generate.py	28.57%	5 Missing ⚠️
piccolo/utils/pydantic.py	66.66%	2 Missing ⚠️
piccolo/apps/sql_shell/commands/run.py	90.90%	1 Missing ⚠️
piccolo/conf/apps.py	88.88%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #905      +/-   ##
==========================================
- Coverage   92.09%   92.03%   -0.07%     
==========================================
  Files         107      107              
  Lines        8126     8145      +19     
==========================================
+ Hits         7484     7496      +12     
- Misses        642      649       +7     

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