Description

If you have variables embedded in payload-file-path JSON data, the variables won't be expanded.

You can do tests with the following:

• https://github.com/slackapi/slack-github-action/blob/main/.github/workflows/main.yml#L94-L101
• https://github.com/slackapi/slack-github-action/blob/main/.github/resources/payload-notification.json

What type of issue is this? (place an x in one of the [ ])

• bug
• enhancement (feature request)
• question
• documentation related
• example code related
• testing related
• discussion

Requirements (place an x in each of the [ ])

• I've read and understood the Contributing guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've searched for any related issues and avoided creating a duplicate issue.