Handle `Errno::ENETUNREACH` in `Gitlab::HTTP`

Handled the same as `Errno::EHOSTUNREACH` is, in `Gitlab::HTTP`. We see
some of these exceptions on occasion being raised by `WebHookService`.
Handling within `Gitlab::HTTP` will mean the service will successfully
disable failing web hooks.

Changelog: changed

lib/gitlab/http.rb

@@ -15,7 +15,7 @@ module Gitlab
     ].freeze
     HTTP_ERRORS = HTTP_TIMEOUT_ERRORS + [
       EOFError, SocketError, OpenSSL::SSL::SSLError, OpenSSL::OpenSSLError,
-      Errno::ECONNRESET, Errno::ECONNREFUSED, Errno::EHOSTUNREACH,
+      Errno::ECONNRESET, Errno::ECONNREFUSED, Errno::EHOSTUNREACH, Errno::ENETUNREACH,
       Gitlab::HTTP::BlockedUrlError, Gitlab::HTTP::RedirectionTooDeep
     ].freeze