Merge in DNS/dnsproxy from fix-279-doh-race to master

Squashed commit of the following:

commit b036e970fbd8c80d1ed73ddbb6f5b07b880a0107
Author: Andrey Meshkov <am@adguard.com>
Date:   Thu Sep 29 15:18:33 2022 +0300

    better comment for getQUICConfig

commit 59f22fa37a0ded8f9996717b214a4a27a59a6750
Author: Andrey Meshkov <am@adguard.com>
Date:   Thu Sep 29 15:13:30 2022 +0300

    fix build with go1.18

commit 8bc66ad87db06314981ed3eae2d7703a8370d74b
Author: Andrey Meshkov <am@adguard.com>
Date:   Thu Sep 29 15:02:08 2022 +0300

    Add a test that specifically covers #279, fixed one more race

commit de0dfe9d9d707dbc1301bf12850e753bb226b76e
Author: Andrey Meshkov <am@adguard.com>
Date:   Thu Sep 29 10:18:56 2022 +0300

    Fixed a race condition in the DoH upstream

    Also, added a test for races in DoH and DoQ upstreams.
    We should also add it in other DNS implementations but only
    after the tests there made to not depend on external services.

    Closes #279