Flatten ORs and ANDs in marker construction (#4260)
## Summary
If we're ORing an OR, we should just append rather than nesting in
another OR.
In my branch, this let us simplify:
```
python_version < '3.10' or python_version > '3.12' or (python_version < '3.8' or python_version > '3.12')
```
To:
```
python_version < '3.10' or python_version > '3.12
```
