patch 8.2.0205: error code E899 used twice

Problem:    Error code E899 used twice.
Solution:   Use E863 for the terminal in popup error.
diff --git a/src/popupwin.c b/src/popupwin.c
index 714f457..c438000 100644
--- a/src/popupwin.c
+++ b/src/popupwin.c
@@ -2873,7 +2873,7 @@
     if (WIN_IS_POPUP(curwin) && curbuf->b_term != NULL
 					   && term_job_running(curbuf->b_term))
     {
-	emsg(_("E899: Not allowed for a terminal in a popup window"));
+	emsg(_("E863: Not allowed for a terminal in a popup window"));
 	return TRUE;
     }
     return FALSE;