patch 9.0.1449: test for prompt buffer is flaky

Problem:    Test for prompt buffer is flaky.
Solution:   Use WaitForAssert() instead of TermWait(). (Ozaki Kiichi,
            closes #12247)
diff --git a/src/version.c b/src/version.c
index ba8b40e..23b39e7 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1449,
+/**/
     1448,
 /**/
     1447,