Move to Golang version 1.21

[skonto]

Proposed Changes

• Needed for Support http1 full duplex per workload #14568
• Moves Golang to 1.21 (latest supported)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (f3e1a2d) 86.03% compared to head (b4d3a3c) 86.02%.
Report is 25 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14641      +/-   ##
==========================================
- Coverage   86.03%   86.02%   -0.01%     
==========================================
  Files         197      197              
  Lines       14916    14929      +13     
==========================================
+ Hits        12833    12843      +10     
- Misses       1774     1775       +1     
- Partials      309      311       +2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[ReToCode]

/lgtm
/approve

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ReToCode, skonto

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [ReToCode,skonto]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment