Fix: missing function clause.

[teesloane]

Describe your changes

Closes #355.

Technically, I suppose I could rename :new_campaign over on the program show.ex file, but I wasn't sure if it was there for a reason (as perhaps having just :new might imply it's for making a :new program ?

Checklist before requesting a review

• I have performed a self-review of my code
• If it is a core feature, I have added tests.
• Are there other PRs or Issues that I should link to here?
• Will this be part of a product update? If yes, please write one phrase
  about this update in the description above.

[mveytsman]

This works but I think it's messy to bring in the new_campaign action from the program into the campaign form component

better would be to change the name of the action to :new when we load this component here: https://github.com/bikebrigade/dispatch/blob/main/lib/bike_brigade_web/live/program_live/show.html.heex#L87

I think that's the better separation of concerns

Adressed requests.