sourcehut portgroup: project name should be included in default distname

[ryandesign (Ryan Carsten Schmidt)]

The sourcehut portgroup sets this default distname:

    git.branch              [join ${sourcehut.tag_prefix}]${sourcehut.version}[join ${sourcehut.tag_suffix}]

    default distname        {${git.branch}}

This is not suitable because it does not include the project name.

This is the reason why, in ​the go directory of the distfiles server, which contains the distfiles of numerous projects that are written in the go language, we have numerous distfiles whose names are only the version number with no indication of what project they belong to:

• 0.2.1.tar.gz (kiln)
• 0.3.0.tar.gz (kiln)
• 0.3.1.tar.gz (kiln)
• 0.3.2.tar.gz (kiln)
• 0.4.0.tar.gz (kiln)
• v0.3.0.tar.gz (hut)
• v0.3.4.tar.gz (ijq)
• v0.3.5.tar.gz (ijq)
• v0.3.6.tar.gz (ijq)
• v0.3.8.tar.gz (ijq)
• v0.4.0.tar.gz (ijq)
• v0.4.1.tar.gz (ijq)

Worse, this could lead to conflicts in the future if any of those projects ever reach a version number any of the other projects had ever reached.

Use a default distname that includes the project name, like kiln-0.2.1 or hut-v0.3.0. If the sourcehut service doesn't offer a URL that provides such a file, fake it with a dummy GET parameter like the github portgroup does.

[ryandesign (Ryan Carsten Schmidt)]

The same issue affects the gitea portgroup; see #68447.