Phone volume buttons can't control VoiceComm output on lock screen

Android version(s): oriole-user 15 AP4A.250105.002.A1 12703047 release-key
Android device(s): Pixel 6
Oboe version: Oboe tester (91) v2.7.2, Oboe version v1.9.3 (debug build from tag 1.9-stable)
App name used for testing: Oboe tester

## Summary
Using background and foreground flags, when you turn power off the device (lock screen), the VoiceComm/Speech output can't handled the volume with the device buttons.

## Steps to reproduce

1. Open oboe tester
2. enable background operation
3. enable foreground operation
4. Go to test output
5. select usage to: VoiceComm
6. select content type to: Speech
7. Open and start the stream output
8. Turn off the device with the power button
9. Try to change the volume (it is impossible)

## Expected behavior

Change the volume in background when the screen is off

## Actual behavior

This is only working when the screen is on. When the device is locked (screen off), you are not able to change the volume.
**Note:** when you not unspecified any "Usage" and "ContentType", everything works fine.

This wrong behavior was reproduced in the next devices:

**Devices**

- OnePlus6 with Android 11
- Pixel6 Oriole with Android 15
- Pixel7 with GrapheneOS

Pixel 6 details:

```bash
ro.product.brand = google
ro.product.manufacturer = Google
ro.product.model = Pixel 6
ro.product.device = oriole
ro.product.cpu.abi = arm64-v8a
ro.build.description = oriole-user 15 AP4A.250105.002.A1 12703047 release-keys
ro.hardware = oriole
ro.hardware.chipname =
ro.arch =
| grep aaudio = [aaudio.hw_burst_min_usec]: [2000]
[aaudio.mmap_exclusive_policy]: [2]
[aaudio.mmap_policy]: [2]
```

OnePlus6 Android 11 details:

```bash
ro.product.brand = OnePlus
ro.product.manufacturer = OnePlus
ro.product.model = ONEPLUS A6003
ro.product.device = OnePlus6
ro.product.cpu.abi = arm64-v8a
ro.build.description = OnePlus6-user 11 release-keys
ro.hardware = qcom
ro.hardware.chipname =
ro.arch =
| grep aaudio =
```