fix(types): align cjs cancelToken types (#7414)

the import/esm types include `undefined` (ref:
https://github.com/axios/axios/blob/v1.x/index.d.ts#L457)

this was added recently in #5560 - but only to `index.d.ts`,
which can break type-checking in projects using a mixture
of cjs and esm, when `exactOptionalPropertyTypes` is enabled,
as it makes the request config types incompatible with eachother.

you can see an example of the type error / this patch resolving
it on https://github.com/mnahkies/openapi-code-generator/pull/427

Co-authored-by: Jay <jasonsaayman@gmail.com>

index.d.cts

@@ -503,7 +503,7 @@ declare namespace axios {
     httpAgent?: any;
     httpsAgent?: any;
     proxy?: AxiosProxyConfig | false;
-    cancelToken?: CancelToken;
+    cancelToken?: CancelToken | undefined;
     decompress?: boolean;
     transitional?: TransitionalOptions;
     signal?: GenericAbortSignal;