patch 8.2.1271: Vim9: Error for Funcref function argument type

Problem:    Vim9: Error for Funcref function argument type.
Solution:   Find the actual function type if possible. (issue #6507)
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 55f08a7..999833b 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -599,6 +599,28 @@
 	member.tt_member = &t_any;
 	actual.tt_member = &member;
     }
+    else if (actual_tv->v_type == VAR_FUNC || actual_tv->v_type == VAR_PARTIAL)
+    {
+	char_u	*name = NULL;
+	ufunc_T *ufunc = NULL;
+
+	if (actual_tv->v_type == VAR_PARTIAL)
+	{
+	    if (actual_tv->vval.v_partial->pt_func != NULL)
+		ufunc = actual_tv->vval.v_partial->pt_func;
+	    else
+		name = actual_tv->vval.v_partial->pt_name;
+	}
+	else
+	    name = actual_tv->vval.v_string;
+	if (name != NULL)
+	    // TODO: how about a builtin function?
+	    ufunc = find_func(name, FALSE, NULL);
+	if (ufunc != NULL && ufunc->uf_func_type != NULL)
+	    actual = *ufunc->uf_func_type;
+	else
+	    actual.tt_member = &t_any;
+    }
     else
 	actual.tt_member = &t_any;
     return check_type(expected, &actual, TRUE);