Fix repo_url concatenation logic in importer

[rmg0070]

Replaced incorrect ends_with usage with Ruby's end_with?

Description

While running the SMT to RMT migration using:

rmt-data-import -d ./

a NoMethodError was encountered due to the use of the non-existent ends_with method on a Ruby String.

Ruby provides end_with?, not ends_with.
This caused the importer to fail while normalizing repository URLs.

This change replaces the incorrect method call with end_with?, ensuring repository URLs are normalized correctly and preventing the runtime error during import.

Related Issue / Ticket / Trello card: N/A (encountered during SMT → RMT migration)

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How to test

1. Prepare an SMT export directory
2. Run:
   rmt-data-import -d ./
3. Verify:
   • Import completes successfully
   • No NoMethodError is raised
   • Repository URLs with and without trailing slashes are handled correctly

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Change Type

• Bug Fix (a non-breaking change which fixes an issue)
• New Feature
• Documentation Update

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Checklist

• I have reviewed my own code and believe that it's ready for an external review.
• I have provided comments for any hard-to-understand code.
• I have documented the MANUAL.md file with any changes to the user experience. (Not applicable)
• I have added a changelog entry to package/obs/rmt-server.changes. (Not required for a trivial fix)

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Review

Please review according to the SUSE code review guidelines:
https://github.com/SUSE/scc-docs/blob/master/team/workflow/code_review.md