Add UT for pkg/discovery

[qiuming-best]

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Fixes #(issue)
Fix #6254
Fix codespell check error

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[codecov-commenter]

Codecov Report

Merging #6394 (e2bb5b3) into main (78025a0) will increase coverage by 0.37%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #6394      +/-   ##
==========================================
+ Coverage   49.88%   50.26%   +0.37%     
==========================================
  Files         227      228       +1     
  Lines       23376    23780     +404     
==========================================
+ Hits        11661    11952     +291     
- Misses      10836    10937     +101     
- Partials      879      891      +12     

Impacted Files	Coverage Δ
pkg/uploader/types.go	100.00% <ø> (ø)
pkg/controller/data_upload_controller.go	66.21% <100.00%> (ø)
pkg/uploader/kopia/snapshot.go	79.71% <100.00%> (ø)
pkg/uploader/provider/kopia.go	85.03% <100.00%> (ø)
pkg/uploader/provider/provider.go	100.00% <100.00%> (ø)

... and 5 files with indirect coverage changes