patch 9.0.0748: Kitty may send key without modifiers with CSI u code

Problem:    Kitty may send key without modifiers with CSI u code.
Solution:   Handle CSI u code without modifiers. (Trygve Aaberge,
            closes #11364)
diff --git a/src/version.c b/src/version.c
index a6e3a5f..d09422b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    748,
+/**/
     747,
 /**/
     746,