patch 8.2.1954: Vim9: not all command modifiers are tested

Problem:    Vim9: not all command modifiers are tested.
Solution:   Add tests for "keep" modifiers.  Fix that marks are lost even
            though ":lockmarks" is used.

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1954,
 /**/
     1953,
 /**/