Install fails on older Ubuntu/Mint due to PyQt6

Since on the binary release I got

```
[21440] Error loading Python lib '/[redacted]/activitywatch-v0.12.0/libpython3.8.so.1.0': dlopen: /[redacted]/libpython3.8.so.1.0: cannot open shared object file: No such file or directory
```

I'm compiling from scratch. This worked on Linux Mint 19.3 for v0.12.0 but failed for v0.12.1 with the following issue:

https://stackoverflow.com/questions/72275959/pip-install-pyqt6-fails-module-sipbuild-api-has-no-attribute-prepare-metadat

The only way I could currently make it work was downgrade the aw-qt submodule to v0.12.0 version using

```
(cd aw-qt && git checkout 730575bc16223a9c030bced07a7851299be33119) && make build
```