Temporary CI fix for npm bug

[aomarks]

Context: npm/cli#4980, lit/lit#3011

[augustjk]

Oh, oops, it's actually not just limited to 16. The default latest patch versions for 14 and 18 also are shipping with the problematic npm.

And the repo setting for required workflow seems like it needs updating.

Perhaps a better alternative might be to change the affected assertions to match rather than equal?

[augustjk]

Or doing the workaround mentioned here actions/runner-images#5716 (comment) as a windows-only workflow step might be worth trying?

[aomarks]

Fixed it by just removing the culprit string from stderr as we report it from the test rig.