patch 8.0.0255: setpos() does not use the buffer argument for all marks

Problem:    When calling setpos() with a buffer argument it often is ignored.
            (Matthew Malcomson)
Solution:   Make the buffer argument work for all marks local to a buffer.
            (neovim #5713)  Add more tests.

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    255,
 /**/
     254,
 /**/