fix(VSpeedDial): avoid position glitch when reopening menu

[J-Sek]

Description

fixes #21017

Markup:

<template>
  <v-app>
    <v-container>
      <!-- rage-click open/close to see if items stay within menu boundaries -->
      <v-fab app icon="mdi-arrow-up" location="bottom center">
        <v-icon />
        <v-speed-dial
          location="top"
          activator="parent"
          transition="slide-y-reverse-transition"
        >
          <v-btn
            v-for="i in 9"
            :key="i"
            prepend-icon="mdi-home"
            color="primary"
            :text="`Hello #${i}`"
            size="small"
          />
        </v-speed-dial>
      </v-fab>
    </v-container>
  </v-app>
</template>