Fix new lint and config errors

[dkotter]

What?

Fixing some new linting and config errors coming out of recent merged PRs

Why?

Want to ensure our GitHub Workflows remain in a passed state

How?

Coming out of #172, I'm seeing the artifacts directory is no longer git-ignored. This directory is added by our E2E tests so we want to ensure this doesn't get committed to our repo. While it would be great if this directory could be nested within our tests directory instead of in the root, I'm running into issues with how wp-scripts runs these tests and having that change work properly. So for now I'm adding this directory back to our gitignore file.

In addition, seeing a new JS lint error and typescripts errors after the merging in of #143. I think this is also due to changes made in #172 and why these errors weren't flagged originally within #143.

There are some minor typescript errors fixed here and the JS lint error is flagging the use of an experimental API which unfortunately we need to use here as it's the only approach to modify the excerpt panel. So this PR ignores that particular error for now.

Testing Instructions

Ensure all workflows pass on this PR

[github-actions]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 47.93%. Comparing base (f21fd0c) to head (ac50afb).
⚠️ Report is 12 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff             @@
##             develop     #176   +/-   ##
==========================================
  Coverage      47.93%   47.93%           
  Complexity       243      243           
==========================================
  Files             22       22           
  Lines           1431     1431           
==========================================
  Hits             686      686           
  Misses           745      745           

Flag	Coverage Δ
unit	47.93% <ø> (ø)

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[dkotter]

@jeffpaul This isn't required for the 0.2.0 release but would be nice to get merged in sooner than later as we'll have a failing lint check on all PRs until this is merged in, just FYI