Fix hacking test with syntax error

This hacking test has a syntax error in it. On older pythons, this
does not prevent us from finding the second popen() use, but on
python 3.12 it does.

Change-Id: Ib74dc030118e0cb9fab548b112d32ce080969a15

nova/tests/unit/test_hacking.py

@@ -517,7 +517,7 @@ class HackingTestCase(test.NoDBTestCase):
                foobar_cmd = "foobar -get -beer"
                answer = os.popen(foobar_cmd).read()
 
-               if answer == nok":
+               if answer == "nok":
                    try:
                        os.popen(os.popen('foobar -beer -please')).read()