Remove superfluous iteration

Co-authored-by: Stanislav Terliakov <50529348+sterliakov@users.noreply.github.com>

Author: m-aciek

mypy/subtypes.py

@@ -538,11 +538,12 @@ def visit_instance(self, left: Instance) -> bool:
             lname = left.type.fullname
 
             # Check if this is an unsafe subtype relationship that should be blocked
-            if self.options and codes.UNSAFE_SUBTYPE in self.options.enabled_error_codes:
-                # Block unsafe subtyping relationships when the error code is enabled
-                for subclass, superclass in UNSAFE_SUBTYPING_PAIRS:
-                    if lname == subclass and rname == superclass:
-                        return False
+            if (
+                self.options
+                and codes.UNSAFE_SUBTYPE in self.options.enabled_error_codes
+                and (lname, rname) in UNSAFE_SUBTYPING_PAIRS
+            ):
+                return False
 
             # Always try a nominal check if possible,
             # there might be errors that a user wants to silence *once*.