fix: broken url to github release in web-ui

[josxha]

Rationale

I noticed that the github release link has an outdated format.

• broken link: https://github.com/maplibre/martin/releases/tag/0.20.1
• actual url: https://github.com/maplibre/martin/releases/tag/martin-v0.20.1

Changes in this PR

• Fixes the github release link
• Open the release page in a new tab to match the behavior of the other header links.
• The tests used v0.0.0-test as mock value, updated it to 0.0.0-test to match the actual format

[Copilot]

Pull Request Overview

This PR updates the GitHub release link for the Martin version badge to include the "martin-v" prefix and opens the link in a new tab.

• Updated the release tag URL format from tag/{version} to tag/martin-v{version} to match the actual GitHub release tag naming convention
• Added target="_blank" to open the version link in a new tab

[CommanderStorm]

Thanks for the report and the fix ❤️