test(encoding/form): add unit test and code style modift

[demoManito]

Description (what this PR does / why we need it):

code style modify

Which issue(s) this PR fixes (resolves / be part of):

part of #2354

Other special notes for the reviewers:

[codecov-commenter]

Codecov Report

Merging #2467 (476750f) into main (dcae38d) will increase coverage by 0.38%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##             main    #2467      +/-   ##
==========================================
+ Coverage   84.91%   85.30%   +0.38%     
==========================================
  Files          88       88              
  Lines        3799     3797       -2     
==========================================
+ Hits         3226     3239      +13     
+ Misses        405      388      -17     
- Partials      168      170       +2     

Impacted Files	Coverage Δ
encoding/form/form.go	65.71% <0.00%> (ø)
encoding/form/proto_decode.go	61.77% <100.00%> (+8.03%)	⬆️
config/file/watcher.go	59.37% <0.00%> (-6.25%)	⬇️
config/file/file.go	61.90% <0.00%> (-4.77%)	⬇️

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