Show resolved URL in duplicate submission error message when relevant

[per1234]

library-registry-submission-parser resolves redirects in the submitted URLs and validates the request for that resolved URL.

One of the validations is checking whether the submitted URL is already in the repositories list. If so, the validation fails and the bot makes a comment on the pull request. In the case where the resolved URL is different from the submitted URL, this failure can be confusing, since the duplicate will not be found in a search for the submitted URL. Previously, the comment from the bot only mentioned the submitted URL.

An example of such a situation can be seen here:

arduino/library-registry#6059 (comment)

A problem was found with your submission https://github.com/styropyr0/SSD1306

❌ ERROR: Submission URL is already in the Library Manager index.

The submitted URL https://github.com/styropyr0/SSD1306 is not present in the repository list, which makes this comment from the bot seem to be incorrect. However, the submitted URL resolved to https://github.com/styropyr0/oled.h, and that URL is present in the list.

The communication about the validation failure under these conditions is hereby improved by using a different error message that explains it is the resolved URL that was found in the list, and states that URL.

In the example above, this change will cause the bot to instead comment:

A problem was found with your submission https://github.com/styropyr0/SSD1306

❌ ERROR: Resolved URL https://github.com/styropyr0/oled.h.git is already in the Library Manager index.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.

Project coverage is 24.68%. Comparing base (4252282) to head (bbe9570).
Report is 90 commits behind head on main.

Files with missing lines	Patch %	Lines
main.go	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #229      +/-   ##
==========================================
- Coverage   29.15%   24.68%   -4.47%     
==========================================
  Files           1        1              
  Lines         271      320      +49     
==========================================
  Hits           79       79              
- Misses        188      237      +49     
  Partials        4        4              

Flag	Coverage Δ
unit	24.68% <0.00%> (-4.47%)	⬇️

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