v6: OpenIdConnectApplicationSettingsClient.UnmarshalJSON rejects real GET responses that omit grant_types

[exitcode0]

Overview

OpenIdConnectApplicationSettingsClient.UnmarshalJSON treats grant_types as required on read.
However, the Okta app okta_atspoke_iam_connector doesn't return grant_types, so the response fails to unmarshal, the same error happens with ListApplications

Repro

package main

import (
    "context"
    "log"
    "os"

    v6okta "github.com/okta/okta-sdk-golang/v6/okta"
)

func main() {
    cfg, _ := v6okta.NewConfiguration(
        v6okta.WithOrgUrl(os.Getenv("OKTA_ORG_URL")),
        v6okta.WithToken(os.Getenv("OKTA_API_TOKEN")),
        v6okta.WithAuthorizationMode("SSWS"),
    )
    client := v6okta.NewAPIClient(cfg)

    _, _, err := client.ApplicationAPI.
        ListApplications(context.Background()).
        Q("okta_atspoke_iam_connector").
        Execute()
    if err != nil {
        log.Fatal(err) // unmarshal failure on okta_atspoke_iam_connector
    }
    log.Fatal("expected unmarshal failure — SDK may have been fixed")
}

Impact

terraform-provider-okta currently works around this with a raw GET + JSON injection of empty grant_types before handing the body to the SDK.
Any non-Terraform v6 consumer calling GetApplication or ListApplications on a tenant with atspoke installed hits the same
crash.