Release notes not included in notification email to distribution groups.

[astromonkee]

Troubleshooting

• [X] I've searched discuss.bitrise.io for possible solutions.
• Which version of the step is effected? 2.x.x
• Is the issue reproducible with the latest version? YES
• Does the issue happen sporadically, or every time? EVERY TIME
• Is the issue reproducible locally by following our local debug guide? YES

Issue description

The release notes will not be included in the notification email sent to the distribution groups if it's not set prior to setting the distribution groups.

Steps to reproduce

1. Run the step with a distribution group and release notes.
2. Check if the email notification for the distribution group contains the release notes.

[astromonkee]

Hi, Any chance I can have feedback on my PR for this issue?