[io grant] Reword "defined as" for &*chdir

To avoid suggestion that `sub &*foo` is valid syntax.

Author: zoffixznet

doc/Type/IO.pod6

@@ -43,7 +43,7 @@ By default, only C<:d> test is performed.
 
 Defined as:
 
-    sub &*chdir(IO() $path --> IO::Path:D)
+    PROCESS:<&chdir> = sub (IO() $path --> IO::Path:D)
 
 Changes value of C<$*CWD> variable to the provided C<$path> and sets
 the process's current directory to the value of