Missed Python_JWT in #5588.

Since verifiesSignature() only succeeds if a call to python_jwt.verify_jwt exists, creating a bool variable is the only way I've found to correlate this declaration to the predicate. (python_jwt.process_jwt is already correlated to python_jwt.verify_jwt by getting the flow from python_jwt.process_jwt's first argument local source to python_jwt.verify_jwt's first argument)