Merge in DNS/dnsproxy from fix-serve-http to master

Squashed commit of the following:

commit 901fe43e51c1854f43bcb5034e488e2f560a3d67
Author: Andrey Meshkov <am@adguard.com>
Date:   Fri Sep 30 16:02:30 2022 +0300

    stabilize race test

commit 302b6609658b51bb3f7b45ec1cc79fde41486032
Author: Andrey Meshkov <am@adguard.com>
Date:   Fri Sep 30 15:48:00 2022 +0300

    improve tests

commit b24c0a05dd9c2f85a94a9c3b21e41a39f28d2a21
Author: Andrey Meshkov <am@adguard.com>
Date:   Fri Sep 30 15:41:27 2022 +0300

    proxy: return ServeHTTP to the Proxy instance