fix(tabs): fixed twice emit input

[FFxSquall]

Description

Motivation and Context

#3560

How Has This Been Tested?

Markup:

<template>
  <v-app>
    <v-content>
      <v-tabs
        slider-color="yellow"
        v-model="model"
        @input="changeInput"
      >
        <v-tab
          v-for="i in 3"
          :key="i"
          :href="`#tab-${i}`"
        >
          Item {{ i }}
        </v-tab>
        <v-tab-item
          v-for="i in 3"
          :key="i"
          :id="`tab-${i}`"
        >
          <v-card flat>
            <v-card-text v-text="text"></v-card-text>
          </v-card>
        </v-tab-item>
      </v-tabs>
    </v-content>
  </v-app>
</template>
<script>
export default {
  data() {
    return {
      model: 'tab-2',
      text:
        'Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.',
    };
  },
  methods: {
    changeInput(val) {
      console.log(val);
    },
  },
};
</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 feature but make things better)

Checklist:

• The PR title is no longer than 64 characters.
• The PR is submitted to the correct branch (master for bug fixes, dev for new features and breaking changes).
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have created a PR in the documentation with the necessary changes.

[codecov]

Codecov Report

Merging #3561 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #3561   +/-   ##
=======================================
  Coverage   83.59%   83.59%           
=======================================
  Files         152      152           
  Lines        3523     3523           
  Branches     1107     1107           
=======================================
  Hits         2945     2945           
  Misses        430      430           
  Partials      148      148

Impacted Files	Coverage Δ
src/components/VTabs/VTabs.js	100% <100%> (ø)	⬆️

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[lock]

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