patch 8.1.0909: MS-Windows: using ConPTY even though it is not stable

Problem:    MS-Windows: using ConPTY even though it is not stable.
Solution:   When ConPTY version is unstable, prefer using winpty. (Ken Takata,
            closes #3949)
diff --git a/src/version.c b/src/version.c
index a6d7add..bc4ae27 100644
--- a/src/version.c
+++ b/src/version.c
@@ -784,6 +784,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    909,
+/**/
     908,
 /**/
     907,