patch 8.2.3903: "gM" does not count tabs as expected

Problem:    "gM" does not count tabs as expected.
Solution:   Use linetabsize() instead of mb_string2cells(). (closes #9409)
diff --git a/src/version.c b/src/version.c
index 55ddb06..7d5d6b5 100644
--- a/src/version.c
+++ b/src/version.c
@@ -750,6 +750,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3903,
+/**/
     3902,
 /**/
     3901,