patch 8.2.4210: window title test fails in some configurations

Problem:    Window title test fails in some configurations.
Solution:   Only run the test if the title can be obtained.

src/testdir/test_functions.vim

@@ -1632,6 +1632,9 @@ endfunc
 
 func Test_setbufvar_keep_window_title()
   CheckRunVimInTerminal
+  if !has('title') || empty(&t_ts)
+    throw "Skipped: can't get/set title"
+  endif
 
   let lines =<< trim END
       edit Xa.txt

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4210,
 /**/
     4209,
 /**/