Fix relative pathing on dns lookups for CalDAV

[MelissaAutumn]

Sentry bug: https://thunderbird.sentry.io/issues/6033683061/?project=4505428124827648&query=is%3Aunresolved%20issue.priority%3A%5Bhigh%2C%20medium%5D&referrer=issue-stream&statsPeriod=14d&stream_index=3

It seems we have an issue with relative paths. I'm unsure if these dns entries are setup incorrectly, or I just made some bad assumptions on how relative pathing worked from my spec read.

It looks like only the relative path is being passed through without it being appended after the hostname. It then breaks in an unrelated function that expects a parsed url to have a hostname key.