patch 8.2.3970: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more errors to errors.h.
diff --git a/src/spellfile.c b/src/spellfile.c
index 4aa60e4..1797663 100644
--- a/src/spellfile.c
+++ b/src/spellfile.c
@@ -6214,7 +6214,7 @@
 
 	if (*curwin->w_s->b_p_spf == NUL)
 	{
-	    semsg(_(e_notset), "spellfile");
+	    semsg(_(e_option_str_is_not_set), "spellfile");
 	    return;
 	}
 	fnamebuf = alloc(MAXPATHL);