Skip gjs-based tests if ASAN is enabled

Skip gjs-based tests if ASAN is enabled

Unfortunately, introspection uses dlopen(), which doesn't quite
work when the DSO is compiled with ASAN but the outer executable
isn't.

Trying to inject LD_PRELOAD=libasan means the outer executable has to
be leak free...which, yeah, I'm not going to get into running ASAN
today on gjs or pygobject.

So, let's skip those tests - ideally, we still run them in some other
context without the sanitizers.  The coverage we have from them is
middling anyways.

Closes: #622
Approved by: jlebon