`update_account` method also updates username, not just display name

[VojtaStruhar]

I'm using the update_account_async method to set the display name of the player. I'm actually fine with the generated username and I don't want to change it.

# profile.name is a string
_client.update_account_async(_session, null, profile.name)

The method in question:

## Update the current user's account on the server.[br]
## - [param p_session] - The session for the user. [br]
## - [param p_username] - The new username for the user. [br]
## - [param p_display_name] - A new display name for the user. [br]
## - [param p_avatar_url] - A new avatar url for the user. [br]
## - [param p_lang_tag] - A new language tag in BCP-47 format for the user. [br]
## - [param p_location] - A new location for the user. [br]
## - [param p_timezone] - New timezone information for the user. [br]
## Returns a task which represents the asynchronous operation.
func update_account_async(p_session : NakamaSession, p_username = null, p_display_name = null,
		p_avatar_url = null, p_lang_tag = null, p_location = null, p_timezone = null) -> NakamaAsyncResult:
	return await _api_client.update_account_async(p_session,
		NakamaAPI.ApiUpdateAccountRequest.create(NakamaAPI, {
			"avatar_url": p_avatar_url,
			"display_name": p_display_name,
			"lang_tag": p_lang_tag,
			"location": p_location,
			"timezone": p_timezone,
			"username": p_username
		}))

Current behavior

Both username and display name are changed set to profile.name.

Expected behavior

Only the display name should change.

[linear]

SDK-893