Update src/app/schemas/simulation_input.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: GioeleB00

src/app/schemas/simulation_input.py

@@ -52,7 +52,7 @@ def check_simulation_time(cls, v: object) -> int: # noqa: N805
             err_msg_type = "the simulation time must be an integer"
             raise ValueError(err_msg_type) # noqa: TRY004
         if v <= 60:
-            err_msg_val = "the simulation must be at least 60seconds"
+            err_msg_val = "the simulation must be at least 60 seconds"
             raise ValueError(err_msg_val)
         return v