[8.19] (backport #18121) feat: bump go to 1.25.1

[mergify]

Motivation/summary

bump to latest stable version

go 1.25 adds native auto maxprocs so we don't need the automaxprocs lib
anymore.

remove dependency and related tests

Checklist

• Update CHANGELOG.asciidoc
• Documentation has been updated

For functional changes, consider:

• Is it observable through the addition of either logging or metrics?
• Is its use being published in telemetry to enable product improvement?
• Have system tests been added to avoid regression?

How to test these changes

Related issues

Blocked until wolfi go 1.25.0 image is published

---

This is an automatic backport of pull request #18121 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 632899a has failed:

On branch mergify/bp/8.19/pr-18121
Your branch is up to date with 'origin/8.19'.

You are currently cherry-picking commit 632899af.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   .go-version
	modified:   NOTICE-fips.txt
	modified:   NOTICE.txt
	modified:   cmd/intake-receiver/go.mod
	modified:   go.sum
	modified:   internal/beatcmd/beat.go
	modified:   internal/beatcmd/beat_test.go
	deleted:    internal/beatcmd/maxprocs.go
	deleted:    internal/beatcmd/maxprocs_test.go
	modified:   systemtest/apmservertest/server.go
	modified:   systemtest/go.mod

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	both modified:   .github/workflows/ci.yml
	both modified:   go.mod
	deleted by us:   integrationservertest/go.mod

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[github-actions]

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