CI: Reduce duplicate pyarrow version testing
We probably don't need to be testing multiple permutations of pyarrow version & Python version in the CI. Instead:

* PY310 builds will test pyarrow version 6 - 10
* PY38 & 39 builds will test pyarrow = 10

Id be more comfortable with testing all versions on python 3.10 or maybe 3.9. 

We will remove support for 3.8 soonish, so I think this makes more sense? > Id be more comfortable with testing all versions on python 3.10 or maybe 3.9.
> 
> We will remove support for 3.8 soonish, so I think this makes more sense?

Makes sense, will run the different versions on 3.10 instead thx @mroeschke 