CI: Reduce duplicate pyarrow version testing

[mroeschke]

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

[phofl]

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?

[mroeschke]

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

[phofl]

thx @mroeschke