Add parens around second argument to tests 4 and 5.

Add parens around second argument to tests 4 and 5.

If a description were to be added to these tests, in the absence of
parentheses the scalar prototype of CORE::not would enforce a scalar context
onto the balance of the statement, leading to apparently anomalous behavior,
viz., the descriptions would not be printed and test 5 would be reported to
FAIL.