core: fix assert when AddDependencyUnitFiles is called with invalid parameter

unit_file_add_dependency() asserts, so check before calling it that the
type is expected, or return EINVAL to the caller.

root@localhost:~# busctl call org.freedesktop.systemd1 /org/freedesktop/systemd1 org.freedesktop.systemd1.Manager AddDependencyUnitFiles "asssbb" 0 uwhatm8 After 1 1

Broadcast message from systemd-journald@localhost (Mon 2025-01-06 18:12:14 UTC):

systemd[1]: Caught <ABRT>, from our own process.

Fixes systemd/systemd#35882

(cherry picked from commit d87dc74)
(cherry picked from commit b679220)
(cherry picked from commit c65056e)
(cherry picked from commit 4d47117)

Author: bluca

src/core/dbus-manager.c

@@ -2820,7 +2820,7 @@ static int method_add_dependency_unit_files(sd_bus_message *message, void *userd
         flags = unit_file_bools_to_flags(runtime, force);
 
         dep = unit_dependency_from_string(type);
-        if (dep < 0)
+        if (dep < 0 || !IN_SET(dep, UNIT_WANTS, UNIT_REQUIRES))
                 return -EINVAL;
 
         r = unit_file_add_dependency(m->runtime_scope, flags, NULL, l, target, dep, &changes, &n_changes);