fix(VFileInput): label click opens dialog twice

[nekosaur]

Description

alternative solution would be to stop click event propagation on textfield label altogether. not sure if that's better or not

Motivation and Context

closes #15888

How Has This Been Tested?

playground

Markup:

<template>
  <v-file-input
    accept="image/*"
    label="Click me when I'm actived"
  ></v-file-input>
</template>

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)