patch 8.2.3197: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move a few more error messages to errors.h.
diff --git a/src/vim9script.c b/src/vim9script.c
index 85d601c..605d0be 100644
--- a/src/vim9script.c
+++ b/src/vim9script.c
@@ -962,7 +962,7 @@
     {
 	if (sv->sv_const != 0)
 	{
-	    semsg(_(e_readonlyvar), name);
+	    semsg(_(e_cannot_change_readonly_variable_str), name);
 	    return FAIL;
 	}
 	ret = check_typval_type(sv->sv_type, value, where);