[release-2.3] 🌱 Bump go version to 1.21

[damdo]

What type of PR is this?
/kind support

What this PR does / why we need it:
Bump go version to 1.21, required by release tooling in the next minor version.

Release note:

Bump go version to 1.21

[damdo]

/assign @nrb @richardcase
/cc @AndiDog

[richardcase]

@damdo - i suspect this will solve the issue from the cherry pick in #4801

[damdo]

@richardcase Yes, that's the plan 👍 Should we merge this first and retest the other one?

[richardcase]

@richardcase Yes, that's the plan 👍 Should we merge this first and retest the other one?

Yes i think so

/lgtm
/approve

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