move all fuzz stuff to _test files

[vagababov]

Fixes #9725

/assign @dprotaso mattmoor

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[codecov]

Codecov Report

Merging #9726 into master will decrease coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #9726      +/-   ##
==========================================
- Coverage   87.99%   87.93%   -0.06%     
==========================================
  Files         177      176       -1     
  Lines        8449     8424      -25     
==========================================
- Hits         7435     7408      -27     
- Misses        771      772       +1     
- Partials      243      244       +1     

Impacted Files	Coverage Δ
pkg/reconciler/configuration/configuration.go	87.50% <0.00%> (-1.67%)	⬇️

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[dprotaso]

Can we actually move the funcs to a fuzzer subpackage

[dprotaso]

That’s what’s we’re gonna do in Knative.dev/pkg and I’ve seen it across the k8s codebase

[dprotaso]

/lgtm