BF: Bug fix to `update_fsl_package`

Don't request a specific build string for packages when running update_fsl_package, as some noarch packages (e.g. FSLeyes) are actually built for each platform (macOS, Linux, Windows), and have the platform encoded into the build string, so matching against the full build string would potentially request a build of the package for the wrong platform. Instead, just match against the build number, which should be all that is needed to request the latest version.