patch 9.0.0363: common names in test files causes tests to be flaky

Problem:    Common names in test files causes tests to be flaky.
Solution:   Use more specific names.
diff --git a/src/testdir/test_ins_complete.vim b/src/testdir/test_ins_complete.vim
index cee6a32..a79a786 100644
--- a/src/testdir/test_ins_complete.vim
+++ b/src/testdir/test_ins_complete.vim
@@ -1226,14 +1226,14 @@
   CheckUnix
   CheckNotRoot
 
-  call writefile(['about', 'above'], 'Xfile')
-  call setfperm('Xfile', '---r--r--')
+  call writefile(['about', 'above'], 'Xunrfile')
+  call setfperm('Xunrfile', '---r--r--')
   new
   set complete=sXfile
   exe "normal! ia\<C-P>"
   call assert_equal('a', getline(1))
   bw!
-  call delete('Xfile')
+  call delete('Xunrfile')
   set complete&
 endfunc