From what I can tell this doesn't currently exist for URL conditions on forms, only date and number of times as refinement criteria. I think you could select the following and pick all the HubSpot pages that currently exist within your account, though this treads into the weird and wacky territory:
If you could somehow add a URL parameter, e.g. ?utm_source=mypage you can add it as a hidden field to your form. It will be written to the contact with the form submission. You can use this option in your workflow's trigger. Make sure to reset this field when you're done so it can work with the next form submission. Update: I have to correct myself. Hidden fields in non-HubSpot forms are not submitted. Sorry!
From what I can tell this doesn't currently exist for URL conditions on forms, only date and number of times as refinement criteria. I think you could select the following and pick all the HubSpot pages that currently exist within your account, though this treads into the weird and wacky territory: