CI: disable visual testing for forks

[jsoref]

Describe the bug
While #1786 disabled visual testing for this repository, it left the workflow enabled for forks.

To Reproduce
Steps to reproduce the behavior:

1. Fork this repository
2. Make a change
3. See error

Expected behavior
If a workflow is disabled for the main repository, it shouldn't be enabled for forks.

Error

Error: TypeError: Cannot read property 'replace' of undefined
    at /home/runner/work/_actions/chromaui/action/v1/action/main.js:2:1611930
    at /home/runner/work/_actions/chromaui/action/v1/action/main.js:2:1610851
    at Object.next (/home/runner/work/_actions/chromaui/action/v1/action/main.js:2:1610956)
    at o (/home/runner/work/_actions/chromaui/action/v1/action/main.js:2:1609670)
Error: Cannot read property 'replace' of undefined

Desktop (please complete the following information):

• OS: Linux

Additional context
Add any other context about the problem here.

[github-actions]

Hi! This issue has been marked as stale because it has been open with no activity for 180 days. You can comment on the issue or remove the stale label to keep it open. If you do nothing, this issue will be closed in 7 days.

[jsoref]

I'll send a PR

[github-actions]

Hi! This issue has been marked as stale because it has been open with no activity for 180 days. You can comment on the issue or remove the stale label to keep it open. If you do nothing, this issue will be closed in 7 days.

[jsoref]

@lesliecdubs this has a PR...