Shard playwright tests into two separate jobs using a matrix

[talldan]

What/Why?

I noticed that Playwright tests are taking around 30 minutes on CI, while each of the Puppeteer tests are taking around 15 minutes. It'd be good to keep them consistent.

This PR tries sharding the playwright tests in a similar way to how we divide up puppeteer jobs. Playwright supports this, so it should be a bit easier.

Hopefully the command I've added will work.

How?

Use a matrix in the github action, to divide tests across two separate machines.

[talldan]

It doesn't seem to have worked.

Playwright 1:

Running 0 tests using 0 workers, shard 1 of 2

=================
 no tests found.
=================

Playwright 2:

Running 0 tests using 0 workers, shard 2 of 2

=================
 no tests found.
=================

edit: kudos to @kevin940726 for spotting a stray }}, which must have been interpreted as the test filename part of the command.

[talldan]

That seems to be working now.

Playwright tests took 19 minutes in that last test run, and puppeteer tests 17 minutes.

We can consider removing a puppeteer machine and adding another playwright one as more tests are migrated.

[github-actions]

Flaky tests detected in 331f068.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/4062162471
📝 Reported issues:

• [Flaky Test] results in two remaining blocks and positions the caret at the end of the second block #39805 in specs/editor/various/block-deletion.test.js

[kevin940726]

LGTM 👍

Not sure how many total parts we should use here, but we can always change that in the future.

[kevin940726]

Looks like we need to change the settings again to mark Playwright - 1 and Playwright - 2 as required. 😅

[talldan]

Looks like we need to change the settings again to mark Playwright - 1 and Playwright - 2 as required. 😅

Ah gosh. Lets do it tomorrow, probably not a great thing to do on the plugin release day, especially the last one before 6.2 😄