Fix linter suggestions

[Fedosin]

Fixes #15755

Proposed Changes

For the specific case described here, we now check for a NotFound error and return an empty list.

Release Note

NONE

[dprotaso]

linter changes are already part of this PR - https://github.com/knative/serving/pull/15922

[dprotaso]

/hold

can you just fix the Check NotFound error when we get certificates in this PR

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 8 lines in your changes missing coverage. Please review.

Project coverage is 80.90%. Comparing base (c50a00d) to head (68ba69c). Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/reconciler/route/route.go	0.00%	7 Missing and 1 partial :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15924      +/-   ##
==========================================
- Coverage   80.98%   80.90%   -0.08%     
==========================================
  Files         210      210              
  Lines       16780    16784       +4     
==========================================
- Hits        13589    13579      -10     
- Misses       2839     2850      +11     
- Partials      352      355       +3     

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[knative-prow-robot]

PR needs rebase.

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[Fedosin]

Just realized that we call List, not Get. List doesn't return NotFound errors, so your fix with //nolint is more correct.