`TriggerPaths` must exist on disk to be properly detected during `Create-PRPackageProperties`

This is a problem. The paths themselves _should not_ need to exist to be resolved as triggering a package if the package triggerPaths exist.

I retained [this build](https://dev.azure.com/azure-sdk/public/_build/results?buildId=4693346&view=results) to highlight the exact issue at play.

- The `save-package-props` steps fully evaluates all packages
- However, we fall back to `template` packages instead of triggering all the `core` packages because the `common/config` file which SHOULD be triggering the core package doesn't exist due to the sparse-checkout setup for the generate_matrix job.

I have submitted a PR to unblock JS, but we should resolve this wonkiness in code as well.