patch 8.1.0206: duplicate test function name

Problem:    Duplicate test function name.
Solution:   Rename both functions.
diff --git a/src/testdir/test_modeline.vim b/src/testdir/test_modeline.vim
index 6e49577..e278c16 100644
--- a/src/testdir/test_modeline.vim
+++ b/src/testdir/test_modeline.vim
@@ -1,6 +1,6 @@
 " Tests for parsing the modeline.
 
-func Test_invalid()
+func Test_modeline_invalid()
   " This was reading before allocated memory.
   call writefile(['vi:0', 'nothing'], 'Xmodeline')
   call assert_fails('split Xmodeline', 'E518:')