patch 8.2.0687: some tests do not work on FreeBSD

Problem:    Some tests do not work on FreeBSD.
Solution:   Enable modeline.  Use WaitFor() in more cases. (Ozaki Kiichi,
            closes #6036)
diff --git a/src/testdir/test_quickfix.vim b/src/testdir/test_quickfix.vim
index 71a0f15..11bdfbe 100644
--- a/src/testdir/test_quickfix.vim
+++ b/src/testdir/test_quickfix.vim
@@ -1708,7 +1708,6 @@
 endfunc
 
 func Test_switchbuf()
-  CheckNotBSD
   call s:create_test_file('Xqftestfile1')
   call s:create_test_file('Xqftestfile2')
   call s:create_test_file('Xqftestfile3')
@@ -1834,6 +1833,7 @@
 
   " If opening a file changes 'switchbuf', then the new value should be
   " retained.
+  set modeline&vim
   call writefile(["vim: switchbuf=split"], 'Xqftestfile1')
   enew | only
   set switchbuf&vim