patch 9.0.0990: callback name argument is changed by setqflist()

Problem:    Callback name argument is changed by setqflist().
Solution:   Use the expanded function name for the callback, do not store it
            in the argument. (closes #11653)

src/testdir/test_quickfix.vim

@@ -6387,5 +6387,17 @@ func Test_info_line_with_space()
   call setqflist([], 'f')
 endfunc
 
+func s:QfTf(_)
+endfunc
+
+func Test_setqflist_cb_arg()
+  " This was changing the callback name in the dictionary.
+  let d = #{quickfixtextfunc: 's:QfTf'}
+  call setqflist([], 'a', d)
+  call assert_equal('s:QfTf', d.quickfixtextfunc)
+
+  call setqflist([], 'f')
+endfunc
+
 
 " vim: shiftwidth=2 sts=2 expandtab