This can be fixed by applying this patch:
--- libssh-0.11.3-1.orig/debian/control 2026-03-18 15:15:18.086623132 +0100
+++ libssh-0.11.3-1/debian/control 2026-03-18 15:16:15.054481072 +0100
@@ -13,7 +13,7 @@
openssh-server <!nocheck>,
pkgconf,
python3:any <!nocheck>,
-Build-Depends-Indep: doxygen <!nodoc>, graphviz <!nodoc>
+Build-Depends-Indep: doxygen <!nodoc>, graphviz <!nodoc>,
doxygen-awesome-css <!nodoc>
Standards-Version: 4.7.2
Rules-Requires-Root: no
Vcs-Git: https://salsa.debian.org/debian/libssh.git
