Fix custom fetch type (#1587)

Co-authored-by: Maurice <[email protected]>

Author: JE-lee

Diff for: .changeset/gorgeous-planes-rhyme.md

@@ -0,0 +1,5 @@
+---
+"openapi-fetch": patch
+---
+
+Fix the custom fetch type

Diff for: packages/openapi-fetch/src/index.d.ts

@@ -19,7 +19,7 @@ export interface ClientOptions extends Omit<RequestInit, "headers"> {
   /** set the common root URL for all API requests */
   baseUrl?: string;
   /** custom fetch (defaults to globalThis.fetch) */
-  fetch?: typeof fetch;
+  fetch?: (request: Request) => ReturnType<typeof fetch>;
   /** global querySerializer */
   querySerializer?: QuerySerializer<unknown> | QuerySerializerOptions;
   /** global bodySerializer */