[release-1.19] [controller] fix depth metrics

[knative-prow-robot]

This is an automated cherry-pick of #3253

[dprotaso]

/lgtm
/approve

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dprotaso, knative-prow-robot

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• controller/OWNERS [dprotaso]

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[codecov]

Codecov Report

❌ Patch coverage is 33.33333% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.61%. Comparing base (9aa1144) to head (0c824e8).
⚠️ Report is 1 commits behind head on release-1.19.

Files with missing lines	Patch %	Lines
controller/queue_metrics.go	0.00%	4 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff                @@
##           release-1.19    #3254      +/-   ##
================================================
- Coverage         74.64%   74.61%   -0.04%     
================================================
  Files               209      209              
  Lines             12025    12026       +1     
================================================
- Hits               8976     8973       -3     
- Misses             2770     2773       +3     
- Partials            279      280       +1     

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