Fix ci:matrix label in CI

[IanVS]

Issue: none

What I did

In my own project, I attempted to set up a similar github workflow, which would not run unless a tag was present. After experimenting a bit, I found that the way the check here in storybook is set up is not correct. The approach in this PR is what I landed on in my own project, and seems to work correctly.

How to test

• Is this testable with Jest or Chromatic screenshots?
• Does this need a new example in the kitchen sink apps?
• Does this need an update to the documentation?

Verify that the unit test matrix does not run on this PR. Add the label, verify that the unit test matrix starts running. Push a commit to the PR, verify that they run again.

[nx-cloud]

☁️ Nx Cloud Report

CI ran the following commands for commit 3d15c11. Click to see the status, the terminal output, and the build insights.

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✅ Successfully ran 1 target

• nx run-many --target=prepare --all --parallel --max-parallel=15 -- --optimized

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[shilman]

LGTM! Thanks for the fix @IanVS 🙏