patch 8.2.0355: Vim9: str_val is confusing, it's a number

Problem:    Vim9: str_val is confusing, it's a number
Solution:   Rename to stnr_val.
diff --git a/src/version.c b/src/version.c
index 1cbe9e2..f494186 100644
--- a/src/version.c
+++ b/src/version.c
@@ -739,6 +739,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    355,
+/**/
     354,
 /**/
     353,