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/vim9compile.c b/src/vim9compile.c
index 2a0ab25..8e8ae3f 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -2477,7 +2477,7 @@
 	    || (check_writable == ASSIGN_FINAL
 					      && sv->sv_const == ASSIGN_CONST))
     {
-	semsg(_(e_readonlyvar), name);
+	semsg(_(e_cannot_change_readonly_variable_str), name);
 	return FAIL;
     }
     return OK;