[Automation] Bump Golang version to 1.21.1

[apmmachine]

Generated automatically with https://github.com/elastic/apm-pipeline-library/actions/runs/6132911758

Blocked by elastic/golang-crossbuild#311

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Bump golang-version to latest version

Update goDefaultVersion 1.21.1

1 file(s) updated with "1.21.1": * vars/goDefaultVersion.groovy

1.21.1

no GitHub Release found for go1.21.1 on "https://github.com/golang/go"

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