regard TemplateLiteral as discriminant property (#44569)

src/compiler/checker.ts

@@ -22031,7 +22031,7 @@ namespace ts {
                     if ((prop as TransientSymbol).isDiscriminantProperty === undefined) {
                         (prop as TransientSymbol).isDiscriminantProperty =
                             ((prop as TransientSymbol).checkFlags & CheckFlags.Discriminant) === CheckFlags.Discriminant &&
-                            !maybeTypeOfKind(getTypeOfSymbol(prop), TypeFlags.Instantiable);
+                            !maybeTypeOfKind(getTypeOfSymbol(prop), TypeFlags.Instantiable & ~TypeFlags.TemplateLiteral);
                     }
                     return !!(prop as TransientSymbol).isDiscriminantProperty;
                 }