MT#55283 fatal Glib warnings during tests

Make all warnings from Glib fatal during system tests (as they already
are during unit tests).

Change-Id: Ibac5c87c0352a9b404e076c047cebf02e891f232

t/auto-test-helper

@@ -8,6 +8,7 @@ shift
 
 rm -rf fake-"$NAME"-sockets
 mkdir fake-"$NAME"-sockets
-LD_PRELOAD=../t/tests-preload.so RTPE_BIN=../daemon/rtpengine TEST_SOCKET_PATH=./fake-"$NAME"-sockets "$@"
+LD_PRELOAD=../t/tests-preload.so RTPE_BIN=../daemon/rtpengine TEST_SOCKET_PATH=./fake-"$NAME"-sockets \
+	G_DEBUG=fatal-warnings "$@"
 test "$(ls fake-"$NAME"-sockets)" = ""
 rmdir fake-"$NAME"-sockets