There's a merged pull request on the void-packages repository

rtl8812au-dkms update to 20210820_1
https://github.com/void-linux/void-packages/pull/51054

Description:
Allows building with 6.9.x

<!-- Uncomment relevant sections and delete options which are not applicable -->

#### Testing the changes
- I tested the changes in this PR: YES

Built and installed on my machine with 6.9.7_1, plugged in dongle and wifi worked.
copied package to another machine on network with 6.9.6_1, installed.  driver loaded but didn't associate with a station, rebooted to 6.9.7_1 and automatically initialized and connected.

<!--
#### New package
- This new package conforms to the [package requirements](https://github.com/void-linux/void-packages/blob/master/CONTRIBUTING.md#package-requirements): **YES**|**NO**
-->

<!-- Note: If the build is likely to take more than 2 hours, please add ci skip tag as described in
https://github.com/void-linux/void-packages/blob/master/CONTRIBUTING.md#continuous-integration
and test at least one native build and, if supported, at least one cross build.
Ignore this section if this PR is not skipping CI.
-->
#### Local build testing
- I built this PR locally for my native architecture, (ARCH-LIBC)
- I built this PR locally for these architectures (if supported. mark crossbuilds):
  - x86_64