[Go] Compilation errors for NOTION.COM api

Found as part of #7774:

Using the source code from 2026-06-17 and this command:

```
.\it\generate-code.ps1 -descriptionUrl https://developers.notion.com/openapi.json -language "go" -dev
.\it\exec-cmd.ps1 -descriptionUrl https://developers.notion.com/openapi.json -language "go"
```

The generated client does not compile:
```
# integrationtest/client/models
client\models\group_by_config_request.go:80:27: cannot use val (variable of type interface{}) as *GroupByConfigRequest_group_by value in argument to result.SetGroupBy: need type assertion
client\models\group_by_config_request.go:85:31: cannot use val (variable of type interface{}) as *GroupByConfigRequest_type value in argument to result.SetTypeEscaped: need type assertion
client\models\group_by_config_response.go:82:27: cannot use val (variable of type interface{}) as *GroupByConfigResponse_group_by value in argument to result.SetGroupBy: need type assertion
client\models\group_by_config_response.go:87:31: cannot use val (variable of type interface{}) as *GroupByConfigResponse_type value in argument to result.SetTypeEscaped: need type assertion
# integrationtest/client/models
client\models\group_by_config_request.go:80:27: cannot use val (variable of type interface{}) as *GroupByConfigRequest_group_by value in argument to result.SetGroupBy: need type assertion
client\models\group_by_config_request.go:85:31: cannot use val (variable of type interface{}) as *GroupByConfigRequest_type value in argument to result.SetTypeEscaped: need type assertion
client\models\group_by_config_response.go:82:27: cannot use val (variable of type interface{}) as *GroupByConfigResponse_group_by value in argument to result.SetGroupBy: need type assertion
client\models\group_by_config_response.go:87:31: cannot use val (variable of type interface{}) as *GroupByConfigResponse_type value in argument to result.SetTypeEscaped: need type assertion
```

The relevant code snippet:

```golang
// GroupByConfigRequest group-by configuration based on property type.
type GroupByConfigRequest struct {
...
// How to group status values. "group" groups by status group (To Do/In Progress/Done), "option" groups by individual option.
group_by *GroupByConfigRequest_group_by
// Whether to hide groups that have no items.
hide_empty_groups *bool
...
// The property type for grouping.
typeEscaped *GroupByConfigRequest_type
}
...

func CreateGroupByConfigRequestFromDiscriminatorValue(parseNode i878a80d2330e89d26896388a3f487eef27b0a0e6c010c493bf80be1452208f91.ParseNode)(i878a80d2330e89d26896388a3f487eef27b0a0e6c010c493bf80be1452208f91.Parsable, error) {
result := NewGroupByConfigRequest()
if parseNode != nil {
mappingValueNode, err := parseNode.GetChildNode("")
if err != nil {
return nil, err
}
if mappingValueNode != nil {
mappingValue, err := mappingValueNode.GetStringValue()
if err != nil {
return nil, err
}
if mappingValue != nil {
}
}
}
if val, err := parseNode.GetEnumValue(ParseGroupByConfigRequest_group_by); val != nil {
if err != nil {
return nil, err
}
result.SetGroupBy(val)
} else if val, err := parseNode.GetEnumValue(ParseGroupByConfigRequest_type); val != nil {
if err != nil {
return nil, err
}
result.SetTypeEscaped(val)

```

This is the json snippet the generates this class:

```json
"groupByConfigRequest": {
"oneOf": [
{
"$ref": "#/components/schemas/selectGroupByConfigRequest"
},
{
"$ref": "#/components/schemas/statusGroupByConfigRequest"
},
{
"$ref": "#/components/schemas/personGroupByConfigRequest"
},
{
"$ref": "#/components/schemas/relationGroupByConfigRequest"
},
{
"$ref": "#/components/schemas/dateGroupByConfigRequest"
},
{
"$ref": "#/components/schemas/textGroupByConfigRequest"
},
{
"$ref": "#/components/schemas/numberGroupByConfigRequest"
},
{
"$ref": "#/components/schemas/checkboxGroupByConfigRequest"
},
{
"$ref": "#/components/schemas/formulaGroupByConfigRequest"
}
],
"description": "Group-by configuration based on property type."
},

```

Run it\generate-code.ps1 and it\exec-cmd.ps1 with the Notion OpenAPI URL and Go language, then inspect the generated client\models\group_by_config_request.go and group_by_config_response.go files. Trace how the groupByConfigRequest oneOf schema is handled and verify that the generated Go client compiles without the reported type errors.

Written by the indexing model from the issue text.