EASI-3176: Upgrade Go version to 121

[OddTomBrooks]

EASI-3176

Changes and Description

• Change Go version from 1.18 to 1.21

How to test this change

PR Author Review Checklist

• Met the ticket's acceptance criteria, or will meet them in a subsequent PR.
• Added or updated tests for backend resolvers or other functions as needed.
• Added or updated client tests for new components, parent components, functions, or e2e tests as necessary.
• Updated the Postman Collection if necessary.

PR Reviewer Guidelines

• It's best to pull the branch locally and test it, rather than just looking at the code online!
• Check that all code is adequately covered by tests - if it isn't feel free to suggest the addition of tests.
• Always make comments, even if it's minor, or if you don't understand why something was done.

[Jdwoodson]

@OddTomBrooks @ClayBenson94 These three linters are all abandoned and have been moved to disabled by default in later versions of golangci-lint
golangci/golangci-lint#1841

I'm going to update our version of golangci-lint in our pre-commit config and see if that resolves the issue.

EDIT You already did this.