Don't delete the html/builds directory

[kevinbackhouse]

I think this is why the links on https://exiv2.org/download.html don't work. We're deleting the html/builds directory, which is where they're copied to by the downloads.sh script.

[Copilot]

Pull Request Overview

This PR fixes broken download links on the exiv2.org website by preventing the deletion of the html/builds directory during the cleanup process. The issue was that the downloads.sh script copies files to this directory, but the workflow was inadvertently removing it.

• Removes $EXIV2WEB/html/builds from the cleanup command to preserve downloaded build artifacts
• Maintains cleanup of temporary files and the html/releases directory

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