Prevent duplicate month conditions in sensor

[Pulpyyyy]

Ensure month condition is added only if not present.

- platform: schedule_state
  name: test jour mois
  default_state: "on"
  events:
    - state: "off"
      months: [11, 12, 1, 2, 3]
      condition:
        - condition: time
          weekday: [mon, tue, wed, thu, fri, sun]