tunnel: fix BadConfigExceptionTest

Fix the test by changing the DNS to a string with an invalid char in the
`invalid-value.conf` test configuration file.

Signed-off-by: Michal Murin <[email protected]>
Signed-off-by: Jason A. Donenfeld <[email protected]>

Author: michal-murin

tunnel/src/test/resources/invalid-value.conf

@@ -1,6 +1,6 @@
 [Interface]
 Address = 192.0.2.2/32,2001:db8:ffff:ffff:ffff:ffff:ffff:ffff/128
-DNS = 192.0.2.0,yes
+DNS = 192.0.2.0,invalid_value
 PrivateKey = TFlmmEUC7V7VtiDYLKsbP5rySTKLIZq1yn8lMqK83wo=
 [Peer]
 AllowedIPs = 0.0.0.0/0, ::0/0