ref: detect migration drift in CI (nonblocking)

[asottile-sentry]

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 90 lines in your changes missing coverage. Please review.

:white_check_mark: All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
tools/migrations/compare.py	0.00%	77 Missing :warning:
tools/migrations/quick_drift_compare.py	0.00%	13 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #93557      +/-   ##
==========================================
+ Coverage   86.80%   88.08%   +1.28%     
==========================================
  Files       10324    10331       +7     
  Lines      594985   595336     +351     
  Branches    23126    23126              
==========================================
+ Hits       516466   524401    +7935     
+ Misses      78026    70442    -7584     
  Partials      493      493              

[asottile-sentry]

the produced squash is flaky somehow! I'm going to try and eliminate the migration cycle with #93582 and see if that fixes the problems here (it should also significantly simplify the squash script too!)