Modify .coveragerc to fix CI coverage

[Jasha10]

Motivation

code coverage CI is failing.
This PR attempts to fix that.

It seems there were two problems with the .coveragerc file:

• when running coverage report, the run.omit setting in .coveragerc was not being picked up. I moved the contents of run.omit to report.omit.
• The omission pattern *tests* was not excluding the tests folder form coverage. I changed *tests* to `/tests/``.

Have you read the Contributing Guidelines on pull requests?

Yes

Test Plan

Verify coverage now succeeds on CI, and that coverage is still measured for the desired omegaconf source directory.