Prevent GitHub workflow "tag, release and publish" to be executed automatically, which kind of "disables" it

[MrChocolatine]

This PR properly "disables" our GitHub workflow "tag, release and publish".

It is true the workflow was already disabled in #278 , but not correctly.
The workflow is still existing, but with no content, which is an invalid syntax for GitHub workflows.
Because of that, we are constantly getting the same error over and over:

• https://github.com/DazzlingFugu/ember-slugify/actions/workflows/tag-release-publish.yml

  [Error: .github#L1](https://github.com/DazzlingFugu/ember-slugify/commit/757ebfde5ba183ddcb9f28a097748ca7d596ece1#annotation_14567186151)
  No event triggers defined in `on`
  

We have 2 alternatives here:

1. To disable the workflow via GitHub web interface

   a. On this page https://github.com/DazzlingFugu/ember-slugify/actions/workflows/tag-release-publish.yml
   b. Click the ... button in the top right corner > Disable workflow

2. To make sure the workflow can only be triggered manually (which is defined by the syntax on: workflow_dispatch in the YAML file)

   This kind of "disables" the workflow as it won't be executed automatically anymore.
   There is no syntax to "really disable" a workflow. (like is_disabled: true for instance)

   See:

   • https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#workflow_dispatch

     To enable a workflow to be triggered manually, you need to configure the workflow_dispatch event

   • https://docs.github.com/en/actions/using-workflows/manually-running-a-workflow

     To run a workflow manually, the workflow must be configured to run on the workflow_dispatch event.

I went for option (2) so we can actually track this change, to see what happened to the workflow.
With option (1), one could not easily know why the workflow does not run.