Fix oauth tests on node 20

[knolleary]

The Oauth tests were passing a URL object to the route.inject functions. This worked fine in Node 18, but broke in Node 20 - it was causing the request to be sent to / rather than the expected route.

I don't know why this broke in node 20; but there were some changes around the implementation of the URL object between 18 and 20.

The docs for inject say the parameter should be a String, so this tidies up the test to pass in the url as a string instead.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.40%. Comparing base (abcfbc4) to head (d1bdebe).
Report is 10 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5024   +/-   ##
=======================================
  Coverage   78.40%   78.40%           
=======================================
  Files         329      329           
  Lines       15478    15478           
  Branches     3574     3574           
=======================================
  Hits        12136    12136           
  Misses       3342     3342           

Flag	Coverage Δ
backend	78.40% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.