[ci] Improve parallelism of yarn test

[poteto]

Stack from ghstack (oldest at bottom):

• [ci] Cleanup #30037
• [ci] Remove circleci check_generated_fizz_runtime job #30036
• [ci] Add new fizz GitHub action #30035
• [ci] Remove circleci yarn_test job #30034
• -> [ci] Improve parallelism of yarn test #30033
• [ci] Add new yarn test GitHub action #30032

This PR adds parallelism similar to our existing circleci setup for
running yarn tests with the various test params. It does this by
sharding tests into $SHARD_COUNT number of groups, then spawning a job
for each of them and using jest's built in --shard option.

Effectively this means that the job will spawn an additional (where n
is the number of test params)

n * $SHARD_COUNT number of jobs to run tests in parallel

for a total of n + (n * $SHARD_COUNT) jobs. This does mean the
GitHub UI at the bottom of each PR gets longer and unfortunately it's
not sorted in any way as far as I can tell. But if something goes wrong
it should still be easy to find out what the problem is.

The PR also changes the ci argument for jest-cli to be an enum instead
so the tests use all available workers in GitHub actions. This will have
to live around for a bit until we can fully migrate off of circleci.

[vercel]

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Name	Status	Preview	Comments	Updated (UTC)
react-compiler-playground	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jun 22, 2024 4:31pm

[react-sizebot]

Comparing: 454fb35...e4b9888

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.js	=	6.68 kB	6.68 kB	=	1.83 kB	1.83 kB
oss-stable/react-dom/cjs/react-dom-client.production.js	=	497.93 kB	497.93 kB	=	89.26 kB	89.26 kB
oss-experimental/react-dom/cjs/react-dom.production.js	=	6.69 kB	6.69 kB	=	1.83 kB	1.83 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js	=	502.75 kB	502.75 kB	=	89.96 kB	89.96 kB
facebook-www/ReactDOM-prod.classic.js	=	597.17 kB	597.17 kB	=	105.33 kB	105.33 kB
facebook-www/ReactDOM-prod.modern.js	=	571.52 kB	571.52 kB	=	101.27 kB	101.27 kB
test_utils/ReactAllWarnings.js	Deleted	62.88 kB	0.00 kB	Deleted	15.69 kB	0.00 kB

Significant size changes

Includes any change greater than 0.2%:

Expand to show

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
test_utils/ReactAllWarnings.js	Deleted	62.88 kB	0.00 kB	Deleted	15.69 kB	0.00 kB

Generated by 🚫 dangerJS against e4b9888