Limit CI parallelism

[JamieMagee]

Code improvement description

Currently, we parallelize the CI checks very heavily. To the point where we are running 100+ GitHub Actions for each PR commit. This is great for getting quick feedback on a PR. However, we very often are rate limited by the GitHub API. This appears as the following error:

HTTP 403: API rate limit exceeded for site ID installation. If you reach out to GitHub Support for help, please include the request ID 2400:2DD0B0:B64BF0:B7C595:6709695F and timestamp 2024-10-11 18:07:27 UTC. 

The main culprits are specs^1 and smoke tests^2.

Instead of having a 1:1 relationship between ecosystem and PR check, and allowing the number of tests to grow unbounded, we should cap the amount of parallelism.

This will, of course, make the checks slower. But I think that its a worthwhile trade-off. And if we're concerned about the speed of CI checks, we can invest in larger GitHub Actions runners^3