Include SCT verification failure details in error message

[bkabrda]

Summary

Fixes #3798 - this includes SCT verification failure details in error message, hence making it easier to debug the failure.

Release Note

Improved the error message that gets printed on SCT verification failure to include more specific details.

Documentation

I don't believe that this requires documentation, due to how small the change is.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 37.67%. Comparing base (2ef6022) to head (9bf0d93).
Report is 167 commits behind head on main.

Files	Patch %	Lines
pkg/cosign/verify_sct.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3799      +/-   ##
==========================================
- Coverage   40.10%   37.67%   -2.44%     
==========================================
  Files         155      201      +46     
  Lines       10044    12436    +2392     
==========================================
+ Hits         4028     4685     +657     
- Misses       5530     7175    +1645     
- Partials      486      576      +90     

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