www/forgejo: Fix non-BINDATA case

DATADIR is still needed for static assets in the non-BINDATA case.
Point StaticRootPath at it. In the BINDATA case (which is the default),
the assets are linked into the binary and StaticRootPath is not used.

PR: 294619
Fixes: 3686ad021c23 ("www/forgejo: Correct AppWorkPAth")
MFH: 2026Q2