feat: allow the use of if condition to trigger github events

[toVersus]

We could add if condition to trigger workflows with all the supported GitHub events. Please refer to the example repository below.
https://github.com/toVersus/github-actions-sandbox

However, when running actionlint on the example repository, it will return the following error:

❯ actionlint
.github/workflows/action.yaml:3:5: unexpected key "if" for "branch_protection_rule" section. expected one of "branches", "branches-ignore", "paths", "paths-ignore", "tags", "tags-ignore", "types", "workflows" [syntax-check]
  |
3 |     if: true
  |     ^~~
(...)

This PR enables the linter to permit the use of if condition for triggering GitHub events.

[rhysd]

I couldn't find documentation for this syntax in any official documents:

• https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions.
• https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows

Would you show some pointer? I'd like to confirm this is officially defined by GitHub.

[toVersus]

I couldn't find documentation for this syntax in any official documents:

Unfortunately, I couldn't find the documentation either, so I demonstrated the behavior using the sample repository.
The specific use case is related to Digger with the following setup.

name: Terraform Digger

on:
  pull_request:
    branches: [ "main" ]
    types: [ closed, opened, synchronize, reopened ]
  issue_comment:
    types: [created]
    if: contains(github.event.comment.body, 'digger')
  workflow_dispatch:

jobs:
  (...)

I understand that this request may not be considered acceptable since it's not documented behavior. In that case, we will proceed by continuing to ignore the specifi linter error using the following command.

actionlint -color -ignore 'unexpected key "if" for "issue_comment" section'

[rhysd]

Okay, I'll ask it at the official forum.

[rhysd]

https://github.com/orgs/community/discussions/108504