Ruff fix: docstring typo

motile/solver.py

@@ -112,7 +112,7 @@ def add_constraint(self, constraint: Constraint) -> None:
         """Add linear constraints to the solver.
 
         Args:
-            constraints:
+            constraint:
                 The :class:`~motile.constraints.Constraint` to add.
         """
         logger.info("Adding %s constraint...", type(constraint).__name__)