Fixed typo in manual.rst unsafeAssign->uncheckedAssign. Fixes part 1 of

#19266 (#19267)

(cherry picked from commit 610516e)

doc/manual.rst

@@ -1899,7 +1899,7 @@ A small example:
 cast uncheckedAssign
 --------------------
 
-Some restrictions for case objects can be disabled via a `{.cast(unsafeAssign).}` section:
+Some restrictions for case objects can be disabled via a `{.cast(uncheckedAssign).}` section:
 
 .. code-block:: nim
     :test: "nim c $1"