patch 8.2.1759: Vim9: Some tests are still using :let

Problem:    Vim9: Some tests are still using :let.
Solution:   Change more declarations to use :var.
diff --git a/src/version.c b/src/version.c
index ed7b449..fe73a92 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1759,
+/**/
     1758,
 /**/
     1757,