Fix a bug in usage of SSL_set1_groups_list()

Apparently, even though the manpage says it returns an int, it
can return a long instead and cause a warning.

Bug not in any released Tor.  Part of #28399

src/common/tortls.c

@@ -1228,7 +1228,7 @@ tor_tls_context_new(crypto_pk_t *identity, unsigned int key_lifetime,
       list = "P-256:P-224";
     else
       list = "P-256:P-224";
-    int r = SSL_CTX_set1_groups_list(result->ctx, list);
+    int r = (int) SSL_CTX_set1_groups_list(result->ctx, list);
     if (r < 0)
       goto error;
   }