Fix typos

Author: DougGregor

stdlib/public/core/Sendable.swift

@@ -11,8 +11,8 @@
 //===----------------------------------------------------------------------===//
 
 /// A type whose metatype can be shared across arbitrary concurrent contexts
-/// without introduce a risk of data races. When a generic type `T` conforms to
-/// `SendableMetatype`, its metatype `T.Type` conforms to `Sendable.  All
+/// without introducing a risk of data races. When a generic type `T` conforms
+/// to `SendableMetatype`, its metatype `T.Type` conforms to `Sendable`.  All
 /// concrete types implicitly conform to the SendableMetatype protocol, so its
 /// primary purpose is in generic code to prohibit the use of isolated
 /// conformances along with the generic type.