Fix tls_test unit test
Commit 11ed7aac refactored the TLS transport code and unit tests. Specifically it added the
tls_test.c file. This file includes
lib/isc/tests/uv_wrap.h but doesn't use the defined
RETURN_RESET macro. Therefore, the variables
__state_uv_udp_connect are initialized but remain unused. This warning is treated as an error in the CI pipeline.