Rollup merge of rust-lang#156479 - ast-ral:dev-missing-space-decrement-strong-count, r=camelid

fix missing space in Rc::decrement_strong_count docs

Author: JonathanBrouwer

library/alloc/src/rc.rs

@@ -1581,7 +1581,7 @@ impl<T: ?Sized> Rc<T> {
     ///
     /// # Safety
     ///
-    /// The pointer must have been obtained through `Rc::into_raw`and must satisfy the
+    /// The pointer must have been obtained through `Rc::into_raw` and must satisfy the
     /// same layout requirements specified in [`Rc::from_raw_in`][from_raw_in].
     /// The associated `Rc` instance must be valid (i.e. the strong count must be at
     /// least 1) when invoking this method, and `ptr` must point to a block of memory