fix(VCalendar): show border for outside date when calendar has event

[SonTT19]

Description

fixes #22516

Markup:

<template>
  <v-app>
    <v-container>
      <p>
        Alright, looks fine, left and right borders on outside days
        <v-icon color="green">mdi-check</v-icon>
      </p>
      <v-calendar ref="calendar1" model-value="2026-01-01"> </v-calendar>

      <p>
        No left and right borders on outside days when the calendar has an
        event.
        <v-icon color="red">mdi-alert</v-icon>
      </p>
      <v-calendar ref="calendar2" model-value="2026-01-01" :events="events">
      </v-calendar>
    </v-container>
  </v-app>
</template>

<script setup>
  import { ref } from "vue";
  const now = new Date(2026, 0, 4);
  const end = new Date(2026, 0, 5);
  const end2 = new Date(2026, 0, 12);
  const start13 = new Date(2026, 0, 13);

  const end15 = new Date(2026, 0, 15);
  const events = [
    {
      name: "Event name",
      start: now,
      end: end2,
      color: "blue",
      timed: false,
    },
    {
      name: "Event name2",
      start: end,
      end: end2,
      color: "blue",
      timed: false,
    },
    {
      name: "Event name5x",
      start: start13,
      end: end15,
      color: "blue",
      timed: false,
    }
  ];
</script>