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

synapse: update to 1.68.0.
https://github.com/void-linux/void-packages/pull/39416

Description:
build-style/python3-*.sh might need more adjusting for this, I already spotted
one problem where rustc consumes the TMPDIR environment variable and breaks the
build process.

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

#### Testing the changes
- I tested the changes in this PR: **briefly**

<!--
#### 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):
  - aarch64-musl
  - armv7l
  - armv6l-musl
-->