fix(VSelectionControl): label opacity matching regular text

[J-Sek]

Description

fixes #18804

• Q: do we need it for v-checkbox-btn as well? I cannot imagine anyone using it with label prop, but it is available nevertheless.

Markup:

<template>
  <v-app theme="dark">
    <v-container>

      <v-checkbox hide-details label="Checkbox"></v-checkbox>
      <v-checkbox hide-details disabled label="Checkbox disabled"></v-checkbox>
      <v-checkbox hide-details :model-value='true' label="Checkbox selected"></v-checkbox>

      <v-switch hide-details label="Checkbox"></v-switch>
      <v-switch hide-details disabled label="Checkbox disabled"></v-switch>
      <v-switch hide-details :model-value='true' label="Checkbox selected"></v-switch>

      <v-radio label="Radio button"></v-radio>
      <v-radio disabled label="Radio button disabled"></v-radio>
      <v-radio :model-value='true' label="Radio button selected"></v-radio>

    </v-container>
  </v-app>
</template>

[KaelWD]

There's also VRadio. I would probably set this in VSelectionControl and remove the redundant error/disabled override

vuetify/packages/vuetify/src/components/VSelectionControl/VSelectionControl.sass

Lines 26 to 29 in 4fd811a

	&--error,
	&--disabled
	.v-label
	opacity: 1