Adding check for unit test coverage

[pgoslatara]

Resolves #

Problem

Solution

Checklist

• [ ] I have run this code in development, and it appears to resolve the stated issue.
• [ ] This PR includes tests, or tests are not required or relevant for this PR.

[github-actions[bot]]

Coverage Report

File	Stmts	Miss	Cover	Missing
src/dbt_bouncer
config_file_validator.py	64	2	97%	87, 93
parsers.py	142	2	99%	195, 453
runner.py	76	4	95%	134, 170–171, 232
utils.py	101	19	81%	42, 47, 136–154, 177
src/dbt_bouncer/checks/manifest
check_models.py	200	1	99%	599
check_unit_tests.py	47	3	94%	107, 158, 210
src/dbt_bouncer/checks/run_results
check_run_results.py	22	2	91%	56–57
TOTAL	1054	33	97%

Tests	Skipped	Failures	Errors	Time
1	0 :zzz:	0 :x:	0 :fire:	12.737s :stopwatch: