fix typo in Sema

Author: mrs1669

include/swift/Sema/CSFix.h

@@ -823,9 +823,9 @@ class ContextualMismatch : public ConstraintFix {
   bool coalesceAndDiagnose(const Solution &solution,
                            ArrayRef<ConstraintFix *> secondaryFixes,
                            bool asNote = false) const override {
-    // If the from type or to type is a placeholer type that corresponds to an
+    // If the from type or to type is a placeholder type that corresponds to an
     // ErrorExpr, the issue has already been diagnosed. There's no need to
-    // produce another diagnostic for the contextual mismatch complainting that
+    // produce another diagnostic for the contextual mismatch complaining that
     // a type is not convertible to a placeholder type.
     if (auto fromPlaceholder = getFromType()->getAs<PlaceholderType>()) {
       if (fromPlaceholder->getOriginator().is<ErrorExpr *>()) {