docs(library/core/src/pin): fix typo "necessarily" -> "necessary"

Author: ruancomelli

library/core/src/pin.rs

@@ -12,7 +12,7 @@
 //! "pinned," in that it has been permanently (until the end of its lifespan) attached to its
 //! location in memory, as though pinned to a pinboard. Pinning a value is an incredibly useful
 //! building block for [`unsafe`] code to be able to reason about whether a raw pointer to the
-//! pinned value is still valid. [As we'll see later][drop-guarantee], this is necessarily from the
+//! pinned value is still valid. [As we'll see later][drop-guarantee], this is necessary from the
 //! time the value is first pinned until the end of its lifespan. This concept of "pinning" is
 //! necessary to implement safe interfaces on top of things like self-referential types and
 //! intrusive data structures which cannot currently be modeled in fully safe Rust using only