Apply suggestions from code review

Co-authored-by: Derek Pierre <derek.pierre@gmail.com>

newsfragments/3570.feature.rst

@@ -1 +1 @@
-Support for conditions based on JWT tokens.
+Support for conditions based on verification of JWT tokens.

nucypher/policy/conditions/jwt.py

@@ -38,7 +38,7 @@ class JWTVerificationCall(ExecutionCall):
 
         @validates("jwt_token")
         def validate_jwt_token(self, value):
-            if value and not is_context_variable(value):
+            if not is_context_variable(value):
                 raise ValidationError(
                     f"Invalid value for JWT token; expected a context variable, but got '{value}'"
                 )