policy: Allow duplicate statements with different effects (#8775)

This allows "Allow" and "Deny" conflicting statements,
where we evaluate to implicit "Deny".

pkg/policy/policy.go

@@ -88,6 +88,10 @@ func (policy Policy) isValid() error {
 
 	for i := range policy.Statements {
 		for _, statement := range policy.Statements[i+1:] {
+			if policy.Statements[i].Effect != statement.Effect {
+				continue
+			}
+
 			principals := policy.Statements[i].Principal.Intersection(statement.Principal)
 			if principals.IsEmpty() {
 				continue