fix: sparse-checkout not disabled on subsequent checkout

[antoineco]

If actions/checkout is invoked once with sparse-checkout and cone mode disabled, core.sparseCheckout remains enabled for all subsequent invocations of actions/checkout.

This PR addresses the problem by explicitly (re)setting core.sparseCheckout to false (which is the workaround I currently use in my workflow via a separate step).

Reproduction:

    steps:
      - uses: actions/checkout@v4
        with:
          ref: mybranch
          sparse-checkout-cone-mode: false
          sparse-checkout: /my.config

     # $ ls
     # /my.config

      - uses: actions/checkout@v4
        with:
          ref: mybranch

     # $ ls
     # /my.config