Update request-digest.ts

When using InjectHeaders, you can set odata=verbose. When pnpjs is updating X-RequestDigest, and calls _api/contextinfo, its using the injected headers, containing odata=verbose, and the code fails to set X-RequestDigest. So forcing to set the Accept parameter correctly, and not using the injected one.

packages/sp/behaviors/request-digest.ts

@@ -47,6 +47,7 @@ export function RequestDigest(hook?: (url: string, init: RequestInit) => IDigest
 
                     digest = await spPost(SPQueryable([this, combine(webUrl, "_api/contextinfo")]).using(JSONParse(),BatchNever()), {
                         headers: {
+                            "Accept": "application/json",
                             "X-PnPjs-NoDigest": "1",
                         },
                     }).then(p => ({