* feat: default token to GitHub token

* fix: use quotes for clarity

Hi,

I've started using your action and it is really useful!

However, their was one use case for me that was not working:

- I have a workflow which temporally build and deploy a version of my app on every `pull_request`.
- I have a second workflow which cleanup the temporary deployment on `pull_request: types: [closed]`.
  - That second workflow call your action to cancel any build runs still running after the PR is closed.

The problem is that it will not cancel the latest build run if I merge that commit directly; since they both have the same SHA.

So I've added an option `allow_matching_sha` (default to `false`) which can disable that check and allow runs with the same sha on other workflows to be cancelled.

So my second workflow looks like this:
```yaml
on:
  pull_request:
    types: [closed]

jobs:
  cleanup-after-pr-closed:
    name: Cleanup After PR Closed
    runs-on: ubuntu-latest
    steps:
      - name: Cancel build runs
        uses: ericmatte/cancel-workflow-action@match-sha
        with:
          allow_matching_sha: true
          workflow_id: '######'
```

Cheers

Co-authored-by: Steven <steven@ceriously.com>

Docs for PR #50