bump go to v1.21

[dprotaso]

No description provided.

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dprotaso

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6df4a9a) 81.80% compared to head (5d47650) 81.80%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2907   +/-   ##
=======================================
  Coverage   81.80%   81.80%           
=======================================
  Files         167      167           
  Lines       10231    10231           
=======================================
  Hits         8369     8369           
  Misses       1614     1614           
  Partials      248      248           

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[nak3]

/lgtm