tests: Add test on set/frozenset equality.

tests/basics/frozenset_set.py

+try:
+    frozenset
+except NameError:
+    print("SKIP")
+    import sys
+    sys.exit()
+
+# Examples from https://docs.python.org/3/library/stdtypes.html#set
+# "Instances of set are compared to instances of frozenset based on their
+# members. For example:"
+print(set('abc') == frozenset('abc'))
+# This doesn't work in uPy
+#print(set('abc') in set([frozenset('abc')]))