fix: correctly replace cache in namespace isolation mode

[alexmt]

Closes #3008

[codecov]

Codecov Report

Merging #3023 into master will increase coverage by 0.01%.
The diff coverage is 76.47%.

@@            Coverage Diff             @@
##           master    #3023      +/-   ##
==========================================
+ Coverage   38.23%   38.24%   +0.01%     
==========================================
  Files         168      168              
  Lines       18142    18142              
  Branches      237      237              
==========================================
+ Hits         6936     6938       +2     
+ Misses      10340    10339       -1     
+ Partials      866      865       -1

Impacted Files	Coverage Δ
controller/cache/cluster.go	64.2% <76.47%> (+0.56%)	⬆️

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