patch 8.1.0506: modeline test fails when run by root

Problem:    Modeline test fails when run by root.
Solution:   Set 'modeline' for the test. (James McCoy, closes #3592)
diff --git a/src/testdir/test_modeline.vim b/src/testdir/test_modeline.vim
index f02c68c..3bde58d 100644
--- a/src/testdir/test_modeline.vim
+++ b/src/testdir/test_modeline.vim
@@ -1,9 +1,12 @@
 " Tests for parsing the modeline.
 
 func Test_modeline_invalid()
-  " This was reading before allocated memory.
+  " This was reading allocated memory in the past.
   call writefile(['vi:0', 'nothing'], 'Xmodeline')
+  let modeline = &modeline
+  set modeline
   call assert_fails('split Xmodeline', 'E518:')
+  let &modeline = modeline
   bwipe!
   call delete('Xmodeline')
 endfunc
diff --git a/src/version.c b/src/version.c
index 5da6027..54b9a6c 100644
--- a/src/version.c
+++ b/src/version.c
@@ -793,6 +793,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    506,
+/**/
     505,
 /**/
     504,