Update to Go 1.21

[axw]

Motivation/summary

Needed for updating elastic-package. script/update_go_version.sh has been updated to use Go 1.21's go get go@major.minor for updating the Go toolchain version. This is a step towards removing the need for gimme.

Checklist

- [ ] Update CHANGELOG.asciidoc
- [ ] Update package changelog.yml (only if changes to apmpackage have been made)

• Documentation has been updated

How to test these changes

N/A

Related issues

#11643

[mergify]

This pull request does not have a backport label. Could you fix it @axw? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-7.17 is the label to automatically backport to the 7.17 branch.
• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit.

NOTE: backport-skip has been added to this pull request.

[axw]

I'll leave this until @simitt is back, someone will get in touch with Snyk about the errors - seems their go.mod parser hasn't been updated to handle Go 1.21 toolchain directives yet.

[mergify]

This pull request is now in conflicts. Could you fix it @axw? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b update-go-1.21 upstream/update-go-1.21
git merge upstream/main
git push upstream update-go-1.21

[axw]

@Mergifyio backport 8.10 8.11

[mergify]

backport 8.10 8.11

❌ No backport have been created

• Backport to branch 8.10 failed

Git reported the following error:

To https://github.com/elastic/apm-server
 ! [rejected]            mergify/bp/8.10/pr-11654 -> mergify/bp/8.10/pr-11654 (non-fast-forward)
error: failed to push some refs to 'https://github.com/elastic/apm-server'
hint: Updates were rejected because the tip of your current branch is behind
hint: its remote counterpart. Integrate the remote changes (e.g.
hint: 'git pull ...') before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.

• #11826 [8.11] Update to Go 1.21 (backport #11654) has been created for branch 8.11