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_file_perm.vim b/src/testdir/test_file_perm.vim
index 1cb09e8..bb6573b 100644
--- a/src/testdir/test_file_perm.vim
+++ b/src/testdir/test_file_perm.vim
@@ -22,9 +22,9 @@
   call assert_equal(1, setfperm('Xtest', 'rwx------'))
   call delete('Xtest')
 
-  call assert_fails("call setfperm(['Xfile'], 'rw-rw-rw-')", 'E730:')
-  call assert_fails("call setfperm('Xfile', [])", 'E730:')
-  call assert_fails("call setfperm('Xfile', 'rwxrwxrwxrw')", 'E475:')
+  call assert_fails("call setfperm(['Xpermfile'], 'rw-rw-rw-')", 'E730:')
+  call assert_fails("call setfperm('Xpermfile', [])", 'E730:')
+  call assert_fails("call setfperm('Xpermfile', 'rwxrwxrwxrw')", 'E475:')
 endfunc
 
 " vim: shiftwidth=2 sts=2 expandtab