rust-ureq autopkgtest fails

The autopkgtest for rust-ureq 2.9.1-3 fails on ubuntu's autopkgtest infrastructure, it passes in Debian. This is blocking the migration of the new versions of rust-cookie and rust-cookie-store from noble proposed to noble release.

6635s autopkgtest [19:37:37]: @@@@@@@@@@@@@@@@@@@@ summary
6635s rust-ureq-2:@ FAIL non-zero exit status 101
6635s rust-ureq-2: PASS
6635s rust-ureq-2:brotli PASS
6635s rust-ureq-2:cookies PASS
6635s rust-ureq-2:default PASS
6635s rust-ureq-2:charset PASS
6635s ureq-2:gzip PASS
6635s rust-ureq-2:http-interop PASS
6635s rust-ureq-2:json PASS
6635s rust-ureq-2:native-certs PASS
6635s rust-ureq-2:native-tls PASS
6635s rust-ureq-2:proxy-from-env FAIL non-zero exit status 101
6635s rust-ureq-2:socks-proxy PASS
6635s rust-ureq-2:tls PASS

The issue seems to be that ubuntu's autopkgtest environment has the http_proxy environment variable set. When then "proxy-from-env" feature is enabled (either explicitly or as part of the "all features" test), ureq picks up this proxy which breaks it's testsuite.

Potential ways forward

1. Somehow strip out said environment variable when running the tests.
2. Simply disable testing with those feature combinations.