ref: fix various types for sentry.monitors

[asottile-sentry]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.04%. Comparing base (fe8da9b) to head (db65a95).
Report is 1 commits behind head on master.

❗ Current head db65a95 differs from pull request most recent head 2729b8e

Please upload reports for the commit 2729b8e to get more accurate results.

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #72892       +/-   ##
===========================================
+ Coverage   47.53%   78.04%   +30.51%     
===========================================
  Files        6628     6604       -24     
  Lines      296612   294421     -2191     
  Branches    51085    50757      -328     
===========================================
+ Hits       140999   229786    +88787     
+ Misses     150499    58303    -92196     
- Partials     5114     6332     +1218     

Files	Coverage Δ
src/sentry/monitors/clock_tasks/check_missed.py	100.00% <100.00%> (+48.48%)	⬆️
.../sentry/monitors/endpoints/base_monitor_details.py	86.55% <100.00%> (+45.37%)	⬆️
...tors/endpoints/organization_monitor_index_stats.py	92.75% <100.00%> (ø)
src/sentry/monitors/serializers.py	98.85% <100.00%> (+18.28%)	⬆️

... and 4108 files with indirect coverage changes