chore(pkg,docs): use a working mirror for archlinux arm64.

[FedeDP]

What type of PR is this?

/kind cleanup /kind documentation

Any specific area of the project related to this PR?

/area pkg /area docs

What this PR does / why we need it:

See https://github.com/falcosecurity/kernel-crawler/pull/196. Also, updated builders documentation after recent changes.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[FedeDP]

/hold The mirror went down right after i opened the kernel-crawler + this PR :/ https://github.com/falcosecurity/kernel-crawler/actions/runs/8566017164/job/23475016449

[poiana]

Issues go stale after 90d of inactivity.

Mark the issue as fresh with /remove-lifecycle stale.

Stale issues rot after an additional 30d of inactivity and eventually close.

If this issue is safe to close now please do so with /close.

Provide feedback via https://github.com/falcosecurity/community.

/lifecycle stale

[FedeDP]

/unhold the mirror is back up! /cc @LucaGuerra

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: FedeDP, LucaGuerra

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