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.
diff --git a/src/version.c b/src/version.c
index a55d2f3..231a4f0 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1954,
+/**/
     1953,
 /**/
     1952,