Print the correct number of "ok" instances in audit email

[amstilp]

Previously, this was printing 0 due to a bug. Now it prints the correct number. Add a test to check for this behavior.

Closes #406

[codecov]

Codecov Report

Merging #409 (eddd975) into main (6ad526f) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #409   +/-   ##
=======================================
  Coverage   99.82%   99.82%           
=======================================
  Files         121      121           
  Lines       22802    22803    +1     
=======================================
+ Hits        22762    22763    +1     
  Misses         40       40           

Files	Coverage Δ
anvil_consortium_manager/__init__.py	100.00% <100.00%> (ø)
...ium_manager/management/commands/run_anvil_audit.py	100.00% <ø> (ø)
anvil_consortium_manager/tests/test_commands.py	98.15% <100.00%> (+0.01%)	⬆️

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