Cloud Messaging can't wake up Whatsapp for notifications while the phone is on battery saver

**Describe the bug**
Even though microg does get the messages, Whatsapp doesn't show the notifications for the messages until battery saver is disabled. I was able to get a temporary fix - allowing WhatsApp unrestricted data/wifi usage while on battery saver. However, this shouldn't be necessary - and I'm unsure if this affects other apps, as I've not been able to test. [This issue](https://github.com/microg/GmsCore/issues/1527) mentions a fix by pushing some files, but these appear to be missing.

**To Reproduce**
Steps to reproduce the behavior:
1. Set up MicroG and turn on Cloud Messaging
2. Turn on battery saver
3. Ask someone to send me a Whatsapp message
4. Nothing happens

5. Turn off battery saver mode
6. Messages arrive all at once.

**Expected behavior**
Messages should arrive instantly.

**Screenshots**
Not applicable

**System**
Android Version: 16
Custom ROM: LineageOS 23.2 Miami

**Additional context**
Add any other context about the problem here.

Start by reproducing Cloud Messaging with Android 16, LineageOS 23.2 Miami, WhatsApp, and battery saver enabled. Trace how background message delivery behaves under battery saver; done when WhatsApp notifications arrive promptly without granting unrestricted data or Wi-Fi access.

Written by the indexing model from the issue text.