patch 8.0.0401: test fails with missing balloon feature

Problem:    Test fails with missing balloon feature.
Solution:   Add check for balloon feature.

src/testdir/test_functions.vim

@@ -468,6 +468,8 @@ func Test_getbufvar()
 endfunc
 
 func Test_balloon_show()
-  " This won't do anything but must not crash either.
-  call balloon_show('hi!')
+  if has('balloon_eval')
+    " This won't do anything but must not crash either.
+    call balloon_show('hi!')
+  endif
 endfunc

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    401,
 /**/
     400,
 /**/