[updatecli] Bump Golang version to 1.21.8

[github-actions]

What

Bump go release version with the latest release.

Further details

See changelog for 1.21.8
Generated automatically with https://github.com/elastic/elastic-agent-autodiscover/actions/runs/8216870501

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Bump golang-version to latest version

Update .go-version

1 file(s) updated with "1.21.8": * .go-version

1.21.8

no GitHub Release found for go1.21.8 on "https://github.com/golang/go"

Update .golangci.yml

1 file(s) updated with "1.21.8": * .golangci.yml

1.21.8

no GitHub Release found for go1.21.8 on "https://github.com/golang/go"

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