patch 9.0.0621: filetype test leaves file behind

Problem:    Filetype test leaves file behind.
Solution:   Add deferred delete flag to writefile(). (Dominique Pellé,
            closes #11249)
diff --git a/src/testdir/test_filetype.vim b/src/testdir/test_filetype.vim
index 6778b7f..b5c7de5 100644
--- a/src/testdir/test_filetype.vim
+++ b/src/testdir/test_filetype.vim
@@ -1233,7 +1233,7 @@
 func Test_m_file()
   filetype on
 
-  call writefile(['looks like Matlab'], 'Xfile.m')
+  call writefile(['looks like Matlab'], 'Xfile.m', 'D')
   split Xfile.m
   call assert_equal('matlab', &filetype)
   bwipe!
diff --git a/src/version.c b/src/version.c
index e264b55..eedf110 100644
--- a/src/version.c
+++ b/src/version.c
@@ -700,6 +700,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    621,
+/**/
     620,
 /**/
     619,