Resolve a compilation warning in test_connection.c

Instead of casting an enum to a void and back, use a string --
that's better C anyway.

Fixes bug 40113; bugfix on 0.2.9.3-alpha.
5 jobs for bug40113_035 in 32 minutes and 5 seconds (queued for 1 minute and 20 seconds)
latest
Status Name Job ID Coverage
  Test
passed debian-distcheck #2237

00:08:03

passed debian-docs #2238

00:05:36

passed debian-hardened #2236

00:13:25

passed debian-integration #2239

00:08:29

passed debian-minimal #2235

00:07:24