Don't use string-search in soap-client (bug#53744)

* lisp/net/soap-client.el (soap-decode-xs-complex-type):
Since soap-client is a core ELPA package and may be used with
Emacs versions older than 28, it cannot use `string-search`;
revert to `string-match`.

lisp/net/soap-client.el

@@ -1937,7 +1937,7 @@ This is a specialization of `soap-decode-type' for
                   (e-name (soap-xs-element-name element))
                   ;; Heuristic: guess if we need to decode using local
                   ;; namespaces.
-                  (use-fq-names (string-search ":" (symbol-name (car node))))
+                  (use-fq-names (string-match ":" (symbol-name (car node))))
                   (children (if e-name
                                 (if use-fq-names
                                     ;; Find relevant children