fix docs typo (#16637)

* fix typo

* fix typo

* Update doc/astspec.txt

doc/astspec.txt

@@ -414,7 +414,7 @@ AST:
 Example code:
 
 .. code-block:: nim
-  macro genRepeatEcho(): stmt =
+  macro genRepeatEcho() =
     result = newNimNode(nnkStmtList)
 
     var forStmt = newNimNode(nnkForStmt) # generate a for statement

doc/manual_experimental.rst

@@ -1710,7 +1710,7 @@ e.g. when rewriting term to same term plus extra content.
 e.g. with given example ``echo("ab")`` will be rewritten just once:
 
 .. code-block:: nim
-  template pwnEcho{echo(x)}(x: expr) =
+  template pwnEcho{echo(x)}(x: untyped) =
     {.noRewrite.}: echo("pwned!")
 
   echo "ab"