test: disable nss-systemd for TEST-22 under ASan

test: disable nss-systemd for TEST-22 under ASan

When running TEST-22 under ASan, there's a chain of events which causes
`stat` to output an extraneous ASan error message, causing following
fail:

```
+ test -d /tmp/d/1
++ stat -c %U:%G:%a /tmp/d/1
==82==ASan runtime does not come first in initial library list; you should either link runtime to your application or manually preload it with LD_PRELOAD.
+ test = daemon:daemon:755
.//usr/lib/systemd/tests/testdata/units/testsuite-22.02.sh: line 24: test: =: unary operator expected
```

This is caused by `stat` calling nss which in Arch's configuration calls
the nss-systemd module, that pulls in libasan which causes the $LD_PRELOAD
error message, since `stat` is an uninstrumented binary.

The $LD_PRELOAD variable is explicitly unset for all testsuite-* services
since it causes various issues when calling uninstrumented libraries, so
setting it globally is not an option. Another option would be to set
$LD_PRELOAD for each `stat` call, but that would unnecessarily clutter
the test code.