Rollup merge of rust-lang#146681 - XrXr:patch-1, r=joboet

Add space after brace in `Box<[T]>::new_uninit_slice` example

Trivial cosmetic change.

Author: jdonszelmann

library/alloc/src/boxed.rs

@@ -640,7 +640,7 @@ impl<T> Box<[T]> {
     /// values[0].write(1);
     /// values[1].write(2);
     /// values[2].write(3);
-    /// let values = unsafe {values.assume_init() };
+    /// let values = unsafe { values.assume_init() };
     ///
     /// assert_eq!(*values, [1, 2, 3])
     /// ```