Explicitly disable security key test on aix51 VM.

We don't know how to build the shared objects required for the security
key tests so skip them.

.github/configs

@@ -221,6 +221,7 @@ esac
 
 case "${TARGET_HOST}" in
     aix*)
+	CONFIGFLAGS="--disable-security-key"
 	# These are slow real or virtual machines so skip the slowest tests
 	# (which tend to be thw ones that transfer lots of data) so that the
 	# test run does not time out.