www/forgejo-lts: 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: 7c546a3a09e0 ("www/forgejo-lts: Correct AppWorkPAth")
MFH: 2026Q2
(cherry picked from commit 6d5d169cad9968a142e928d69e95438aafd95774)