cherry-pick: 4517 warning wording

Merge in DNS/adguard-home from 4517-warning-label to master

Updates #4517.

Squashed commit of the following:

commit 4987f63
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Mon Aug 1 13:59:28 2022 +0300

    client: imp wording

client/src/__locales/en.json

@@ -222,7 +222,7 @@
     "updated_upstream_dns_toast": "Upstream servers successfully saved",
     "dns_test_ok_toast": "Specified DNS servers are working correctly",
     "dns_test_not_ok_toast": "Server \"{{key}}\": could not be used, please check that you've written it correctly",
-    "dns_test_warning_toast": "Server \"{{key}}\" does not respond to test requests and may not work properly",
+    "dns_test_warning_toast": "Upstream \"{{key}}\" does not respond to test requests and may not work properly",
     "unblock": "Unblock",
     "block": "Block",
     "disallow_this_client": "Disallow this client",