patch 8.2.1918: Vim9: E1100 mentions :let

Problem:    Vim9: E1100 mentions :let.
Solution:   Mention "var". (closes #7207)
diff --git a/src/version.c b/src/version.c
index 32c42a0..a7508ca 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1918,
+/**/
     1917,
 /**/
     1916,