Fix: Maestro digital post-notification sender label is set incorrectly

[jekuaitk]

As per MaestroHelper::sendNotificationDigitalPost both message and sender label is set to the configured Maestro notification subject.

In fact, the configured sender label is never used.

This results in recipients receiving Digital post with the same sender- and message label.

[jekuaitk]

Hi @ds-bellcom

We just had another reported issue that we would like your review on :-)

[ds-bellcom]

@jekuaitk review is done now 😀

[ds-bellcom]

@jekuaitk Review is done (2 weeks ago). Will you merge it and close this issue when done?

CC: @Anna-itk @ChatBotBerg