patch 8.2.0708: Vim9: constant expressions are not simplified

Problem:    Vim9: constant expressions are not simplified.
Solution:   Simplify string concatenation.
diff --git a/src/version.c b/src/version.c
index c004e33..14504da 100644
--- a/src/version.c
+++ b/src/version.c
@@ -747,6 +747,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    708,
+/**/
     707,
 /**/
     706,