dbt-core CI cannot be skipped

### Housekeeping

- [X] I am a maintainer of dbt-common

### Short description

Using the `Skip Core Testing` label does not trigger the tests to get skipped in [ci_dbt_core_testing.yml](https://github.com/dbt-labs/dbt-common/blob/main/.github/workflows/ci_dbt_core_testing.yml(

### Acceptance criteria

When the label gets added to a PR, all core tests gets skipped

### Suggested Tests

Manually tests you can skip tests.

Ensure you test the tests are skipped during merge as well.

### Impact to Other Teams

None

### Will backports be required?

No

### Context

We need to be able to skip core tests when we're changing something like dependency pins. Since we share pins between the two repos this would make it easier to resolve the multiple PRs.