Add quality checks on pull requests

[nozzlegear]

Once the move to Github Actions gets merged (#745), I plan to implement another action with some simple quality checks that will scan each new pull request for common issues.

Some ideas:

• If a new service class is created, check that it has an accompanying unit test.
• If a new unit test file is created, check that it has a Category trait attribute.
• Check that all unit test files have a test fixture that implements IAsyncLifetime.
  • count (rg "public .*_Fixture .\$") = 0
• Do a rudimentary check that all new .*Service instances in a test file have an equal number of execution policies set.
  • count (rg "new .*Service") = count (rg "SetExecutionPolicy")