patch 8.0.0604: gF test fails still on MS-Windows

Problem:    gF test fails still on MS-Windows.
Solution:   Use : before the line number and remove it from 'isfname'.
diff --git a/src/testdir/test_gf.vim b/src/testdir/test_gf.vim
index d5bdfab..ef1bf10 100644
--- a/src/testdir/test_gf.vim
+++ b/src/testdir/test_gf.vim
@@ -38,7 +38,8 @@
   w! Xfile
   close
   new
-  call setline(1, ['one', 'Xfile@3', 'three'])
+  set isfname-=:
+  call setline(1, ['one', 'Xfile:3', 'three'])
   2
   call assert_fails('normal gF', 'E37:')
   call assert_equal(2, getcurpos()[1])
@@ -47,6 +48,7 @@
   call assert_equal('Xfile', bufname('%'))
   call assert_equal(3, getcurpos()[1])
 
+  set isfname&
   call delete('Xfile')
   call delete('Xfile2')
   bwipe Xfile