Use self-hosted x86 runners

[locallycompact]

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• CHANGELOG updated or not needed
• Documentation updated or not needed
• Haddocks updated or not needed
• No new TODOs introduced or explained herafter

[ch1bo]

Suggested change

	runs-on: [self-hosted, Linux, X86]
	runs-on: [Linux, X64]

For the others, I'd also suggest to use [Linux, X64] instead of explorer as it is more specific on what the job needs, i.e. it will get scheduled on any similar runners (if we add them).

[v0d1ch]

We need to resolve this issue before we can use self hosted runners.