- For regular non-image nonvideo links, they should be made relative,
this was done against `r.Ctx.Links.Base`, but since 637451a45e, that
should instead be done by `SrcLink()` if there's branch information set
in the context, because branch and treepath information are no longer
set in `r.Ctx.Links.Base`.
- This is consistent with how #2166 _fixed_ relative links.
- Media is not affected, `TestRender_Media` test doesn't fail.
- Adds unit tests.
- Ref https://codeberg.org/Codeberg/Community/issues/1485
