fix: remove dummy digest and add comparison logic

[chansuke]

trafficstars

Removed dummy digest for workaround add comparison logic

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 22.22222% with 7 lines in your changes missing coverage. Please review.

Project coverage is 63.27%. Comparing base (4f64086) to head (43ad8da).

Files with missing lines	Patch %	Lines
pkg/argocd/update.go	22.22%	6 Missing and 1 partial :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1161      +/-   ##
==========================================
- Coverage   63.34%   63.27%   -0.07%     
==========================================
  Files          15       15              
  Lines        2357     2358       +1     
==========================================
- Hits         1493     1492       -1     
- Misses        769      771       +2     
  Partials       95       95              

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[chengfang]

@chansuke Can you describe the problem or bug caused by the current code?

[chansuke]

@chengfang sorry for the late reply :pray: the current code mutates image state by setting a "dummy" digest value as a workaround to force updates when using digest strategy with tag-based images, which is a hack that could cause unexpected side effects