Get rid of .format to make ruff happy

Our pipelines are currently failing because of a recent change to ruff: https://github.com/astral-sh/ruff/pull/10238

This would be my way of fixing that. We can obviously also just ignore the new rule, but I personally agree with it. I hadn't seen .format in years before looking at castellum

Tried to have some consistency in how urls are broken up, by having it always be after the study primary key.