patch 8.2.2309: 0o777 not recognized as octal

Problem:    0o777 not recognized as octal.
Solution:   Use vim_isodigit(). (Ken Takata, closes #7633, closes #7631)
diff --git a/src/version.c b/src/version.c
index f39a0d3..f4a1d58 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2309,
+/**/
     2308,
 /**/
     2307,