[8.10](backport #36597) [Automation] Bump Golang version to 1.20.8

[mergify]

This is an automatic backport of pull request #36597 done by Mergify.
Cherry-pick of 4a09ff7 has failed:

On branch mergify/bp/8.10/pr-36597
Your branch is up to date with 'origin/8.10'.

You are currently cherry-picking commit 4a09ff7f44.
  (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:   .golangci.yml
	modified:   CHANGELOG.next.asciidoc
	modified:   auditbeat/Dockerfile
	modified:   dev-tools/kubernetes/filebeat/Dockerfile.debug
	modified:   dev-tools/kubernetes/heartbeat/Dockerfile.debug
	modified:   dev-tools/kubernetes/metricbeat/Dockerfile.debug
	modified:   heartbeat/Dockerfile
	modified:   metricbeat/Dockerfile
	modified:   metricbeat/module/http/_meta/Dockerfile
	modified:   metricbeat/module/nats/_meta/Dockerfile
	modified:   metricbeat/module/vsphere/_meta/Dockerfile
	modified:   packetbeat/Dockerfile
	modified:   x-pack/functionbeat/Dockerfile
	modified:   x-pack/metricbeat/module/stan/_meta/Dockerfile

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   libbeat/docs/version.asciidoc

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

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[elasticmachine]

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• Start Time: 2023-09-20T18:46:32.870+0000

• Duration: 125 min 18 sec

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Test	Results
Failed	0
Passed	27798
Skipped	1987
Total	29785

💚 Flaky test report

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[cmacknz]

Service 'kibana' failed to build: manifest for docker.elastic.co/kibana/kibana:8.10 not found: manifest unknown: manifest unknown

Hmm the version likely needs to be bumped to 8.10.1