patch 8.2.4008: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more error messages to errors.h.
diff --git a/src/syntax.c b/src/syntax.c
index 6e1feb5..7758254 100644
--- a/src/syntax.c
+++ b/src/syntax.c
@@ -4882,7 +4882,7 @@
 			    break;
 			if (p[1] == NUL)
 			{
-			    semsg(_("E789: Missing ']': %s"), kw);
+			    semsg(_(e_error_missing_rsb_str), kw);
 			    goto error;
 			}
 			if (p[1] == ']')