fix typos

Author: thanhnguyen-aws

doc/src/challenges/0023-vec-pt1.md

@@ -65,7 +65,7 @@ Verify the memory safety of the following public functions in (library/alloc/src
 
 The verification must be unbounded---it must hold for slices of arbitrary length.
 
-The verification must be hold for generic type `T` (no monomorphization).
+The verification must hold for generic type `T` (no monomorphization).
 
 ### List of UBs
 

doc/src/challenges/0024-vec-pt2.md

@@ -51,7 +51,7 @@ and the following functions from other files:
 
 The verification must be unbounded---it must hold for slices of arbitrary length.
 
-The verification must be hold for generic type `T` (no monomorphization).
+The verification must hold for generic type `T` (no monomorphization).
 
 ### List of UBs