Updates the Stan submodule to bff119a5d.

stan-buildbot · stan-buildbot · commit e87dc5b910fb · 2025-04-19T12:21:19.000-04:00
diff --git a/StanHeaders/inst/include/upstream b/StanHeaders/inst/include/upstream
@@ -1 +1 @@
-Subproject commit 6ec4b0be48cbfe2ee67d67197f448f80d1254575
+Subproject commit bff119a5dc8e6bc8afd4a82b5ccee5971cd89fde
