Downgrade go to 1.21 due to build image version

[bryantbiggs]

Description

• Downgrade go to 1.21 due to build image version
  • Due to these remnants which need to be resolved first

On a bright note, look how few changes are required for changing a go version 🎉 (was only 4 lines, but the way the CI lint check works, had to run make build to give it something to check 😐 )

Checklist

• Added tests that cover your change (if possible)
• Added/modified documentation as required (such as the README.md, or the userdocs directory)
• Manually tested
• Made sure the title of the PR is a good description that can go into the release notes
• (Core team) Added labels for change area (e.g. area/nodegroup) and kind (e.g. kind/improvement)

BONUS POINTS checklist: complete for good vibes and maybe prizes?! 🤯

• Backfilled missing tests for code in same general area 🎉
• Refactored something and made the world a better place 🌟

[bryantbiggs]

closing in favor of #8157 for now