patch 8.2.3961: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more errors to errors.h.
diff --git a/src/spell.c b/src/spell.c
index 857a793..17b3ff8 100644
--- a/src/spell.c
+++ b/src/spell.c
@@ -4378,7 +4378,7 @@
 	l = (int)STRLEN(curwin->w_s->b_p_spf);
 	if (l > 0 && (l < 4
 			|| STRCMP(curwin->w_s->b_p_spf + l - 4, ".add") != 0))
-	    errmsg = e_invarg;
+	    errmsg = e_invalid_argument;
     }
 
     if (errmsg == NULL)
@@ -4416,7 +4416,7 @@
 	    if (synblock->b_cap_prog == NULL)
 	    {
 		synblock->b_cap_prog = rp; // restore the previous program
-		return e_invarg;
+		return e_invalid_argument;
 	    }
 	}
     }