Update src/client/streamableHttp.ts

nullish coalescing operator ?? instead of the logical OR operator || to handle the case where this?._eventSourceInit?.fetch or this._fetch might be null or undefined but not falsy

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

src/client/streamableHttp.ts

@@ -209,7 +209,7 @@ export class StreamableHTTPClientTransport implements Transport {
         headers.set("last-event-id", resumptionToken);
       }
 
-      const response = await (this._fetch ?? fetch)(this._url, {
+const response = await (this._fetch ?? fetch)(this._url, {
         method: "GET",
         headers,
         signal: this._abortController?.signal,