Add patch to adjust proxy tests to changes in libhttp-proxy-perl.

libhttp-proxy-perl, since 0.304-4, supports IPv6, so when running on the
default 'localhost', this can be 127.0.0.0/8 or ::1. Adjust the three
proxy-using tests to run the proxy server explicitly on 127.0.0.1, as that's
what the rest of the test code expects.

Closes: #924859