CI: misc cleanup & fixes

[bayandin]

Problem

A bunch of small fixes and improvements for CI, that are too small to have a separate PR for them

Summary of changes

• CI(build-and-test): fix parenthesis
• CI(actionlint): fix path to workflow file
• CI: remove default args from actions/checkout, see https://github.com/actions/checkout/tree/v4?tab=readme-ov-file#usage
• CI: remove gen3 label, using a couple self-hosted + small{,-arm64}/large{,-arm64} is enough
• CI: prettify Slack messages, hide links behind text messages
• C(build-and-test): add more dependencies to conclusion job

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[github-actions]

2156 tests run: 2087 passed, 0 failed, 69 skipped (full report)

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Code coverage* (full report)

• functions: 32.3% (7163 of 22173 functions)
• lines: 50.3% (57935 of 115214 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
06b6de2 at 2024-08-14T13:06:29.420Z :recycle:}

[a-masterov]

Looks good.