increase python version to 3.10 for actions

[marqh]

@amilan17

it looks like github have deprecated the python version used in the github actions

the docs recommend always setting this, for consistency, so this is a change that requires occasional management https://github.com/marketplace/actions/setup-python

i have proposed '3.10' taking the suggested default from the github docs

[marqh]

okay, this is progress, the action is running, but hitting a permissions issue

I'll try to check the error code, but it's possible this needs to be a PR from an in-repository branch, not from a fork, in order for the push to authorise

Are you happy for me or someone else to recreate this PR on a branch within this repository?

[amilan17]

@marqh it's fine with me if you want to create a branch in the repo. Thanks for looking into this!

[marqh]

replaced by #469