fix(css): change importance of disabled color of vicon in label tag

[korkt-kim]

Description

fixes #14050

Expected Behavior
even if the v-checkbox is disabled, the v-icon in label should be in red color like the side text.

Actual Behavior
the v-icon in v-checkbox is in "grey" color. this is due to the fact the checkbox is a icon too and a special class is apply to render "disabled". This css class is apply to the v-icon in label which is incorrect.

Motivation and Context

expected behavior will come up

How Has This Been Tested?

local env , visually

Markup:

<template>
  <v-container fluid>
    <v-row>
      <v-col cols="12" sm="4" md="4">
        <v-checkbox v-model="ex4" disabled
          ><template #label
            ><v-icon>mdi-auto-fix</v-icon> <span>no color both</span></template
          ></v-checkbox
        >

        <v-checkbox v-model="ex4" disabled
          ><template #label
            ><v-icon class="red--text">mdi-auto-fix</v-icon>
            <span>only icon has color red</span></template
          ></v-checkbox
        >
      </v-col>
      <v-col cols="12" sm="4" md="4">
        <v-checkbox v-model="ex4" disabled
          ><template #label
            ><v-icon>mdi-auto-fix</v-icon>
            <span class="green--text">only text has color green</span></template
          ></v-checkbox
        >
        <v-checkbox v-model="ex4" disabled
          ><template #label
            ><v-icon class="indigo--text">mdi-auto-fix</v-icon>
            <span class="blue--text">both has color</span></template
          ></v-checkbox
        >
      </v-col>
    </v-row>
  </v-container>
</template>

<script>
export default {};
</script>

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Improvement/refactoring (non-breaking change that doesn't add any features but makes things better)

Checklist:

• The PR title is no longer than 64 characters.
• The PR is submitted to the correct branch (master for bug fixes and documentation updates, dev for new features and backwards compatible changes and next for non-backwards compatible changes).
• My code follows the code style of this project.
• I've added relevant changes to the documentation (applies to new features and breaking changes in core library)