Upstreaming from https://phabricator.wikimedia.org/T132335

Steps to reproduce:

1. Phorge at a579a974ebfe8e91f98a34d2e5269a91c5307cb7, PHP 8.3.7
2. As a Phorge admin, set policy.allow-public to true
3. Create a Maniphest task T4 with a public View Policy.
4. In a private browser window while not being logged in, go to T4 and hover over the Log In button in the top bar: Its URL is http://phorge.localhost/auth/start/?next=%2FT4
5. Scroll down to the bottom of T4 (I do not know why https://we.phorge.it/ does not show a Log In to Comment button at the bottom of a task) and hover over the Log In to Comment button: Its URL is http://phorge.localhost/login/?next=, missing a parameter value.

Expected outcome:
Click the Log In to Comment button, log in, and end up on the page of the object where you clicked the Log In to Comment button - this would be the same behavior as clicking the Log In button in the top bar.

Actual outcome:
Click the Log In to Comment button, log in, and end up on Phorge frontpage. Now click the Back button in your browser a few times to go to the task that you wanted to comment on.