I found the news from the Android Police, that Google added the new Google Play Services and Gboard beta sign-up feature to Google Play Store app.
If you wanted to be a part of beta tester, so It's probably good news for you.
Invitation looks like below.
As we all know that Play Store helps us to get the new features and updates of our favorite apps and games as soon as possible. Today Google added the Play Services and Gboard in the list.
Just a few clicks and you can be running the latest goodies (and maybe some bugs) early.
Google Play Services is the most important and most useful app for the Android device. As we all know that it bundles up a ton of important features and services in Google Play Services. That's why a technical Android user always keeps their eyes on the latest and compatible Google Play services updates for the best native support and new features.
Google also do care for their Android users and always keep releasing the Play Services app with bug fixes and new features.
First you need to get the latest Play Store update to get this feature.
Click below to Download the Play Store v 7.5.25 APK Update
Download the Play Store v 7.5.25 APK
If you want to be a part of the Google Play Services beta team follow the below link and confirm your participation.
Google Play Services Beta Testing Program
Once you be part of the beta tester team, your phone will automatically download the latest beta updates on your phone and will notify you change-logs of the update.
If you ever want to stop getting beta updates, return to the testing page and leave the beta. Then either wait for the stable channel to catch up or manually roll back Play Services (Android Device Manager should be disable from the Administrator menu first).
The Same link is here to be a part of a Gboard Beta testing team.
GBoard Beta Testing Program
Gboard Beta Testing APK Update to Download