Respect branch info for relative links (#28909) (#28922)

Backport #28909 by @KN4CK3R

Fix #28904

Co-authored-by: KN4CK3R <admin@oldschoolhack.me>

modules/markup/markdown/goldmark.go

@@ -137,6 +137,8 @@ func (g *ASTTransformer) Transform(node *ast.Document, reader text.Reader, pc pa
 				var base string
 				if ctx.IsWiki {
 					base = ctx.Links.WikiLink()
+				} else if ctx.Links.HasBranchInfo() {
+					base = ctx.Links.SrcLink()
 				} else {
 					base = ctx.Links.Base
 				}