fix(secret): don't apply unset fields

[wass3r]

fixes go-vela/community#1058

applies to images/repo lists

[codecov]

Codecov Report

❌ Patch coverage is 68.00000% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.33%. Comparing base (15bda2c) to head (3cb3709).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
command/secret/update.go	66.66%	4 Missing and 2 partials ⚠️
action/secret/update.go	71.42%	1 Missing and 1 partial ⚠️

❌ Your project status has failed because the head coverage (71.33%) is below the target coverage (90.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #630      +/-   ##
==========================================
- Coverage   71.44%   71.33%   -0.12%     
==========================================
  Files         174      174              
  Lines        4718     4727       +9     
==========================================
+ Hits         3371     3372       +1     
- Misses       1042     1047       +5     
- Partials      305      308       +3     

Files with missing lines	Coverage Δ
action/secret/secret.go	80.00% <ø> (ø)
action/secret/update.go	76.25% <71.42%> (-1.09%)	⬇️
command/secret/update.go	73.68% <66.66%> (-14.56%)	⬇️

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