chore(tests): Avoid mocking internal compiler state to test phase actions

[Johnnei]

Rewire ScapegoatPhaseTest to run Dotty instead of trying to mock the internal state of the compiler well enough to be able to test it directly. This will fix the errors caused by upgrading to 3.6.2 in #904

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.95%. Comparing base (fa90063) to head (8bd2d29).
Report is 66 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #909      +/-   ##
==========================================
- Coverage   88.08%   83.95%   -4.14%     
==========================================
  Files         142       21     -121     
  Lines        1578      324    -1254     
  Branches      278       31     -247     
==========================================
- Hits         1390      272    -1118     
+ Misses        188       52     -136     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[Johnnei]

@saeltz Please help review this one. I've tested it locally with 3.6.2 but didn't include that part to keep the change isolated.

[saeltz]

Would you please revert the unrelated formatting changes in the inspection file?

[Johnnei]

Would you please revert the unrelated formatting changes in the inspection file?

Done. Probably worth to add scalafmtCheck into the additional checks job as that file got reformatted from an scalafmtAll to clean up my change.

[saeltz]

Thanks! Created #911.