Add lint workflow_call input conflict with required and default

[sksat]

I want to lint below invalid reusable workflow

on:
  workflow_call:
    inputs:
      test_input:
        description: test
        type: string
        required: true  # set this input is required
        default: a      # but default value is provided

When we call this workflow without test_input, it results like this. I made this mistake sometimes.

The workflow is not valid. Input test_input is required, but not provided while calling.

[rhysd]

Thank you for adding the check. It makes sense to me. I may tweak the error message later. CI is broken, but it is not related to changes by this PR. Merging.

[rhysd]

This change was included in the latest release v1.6.14.

[sksat]

Sorry, I forgot to add tests... I'll be careful next time. Thanks for release!