Test on Python 3.10

[MichaelClerx]

#1434

• Now testing on Python 3.10
• Updated rest of 3.9 tests to just use whatever the latest supported version is

@fcooper8472 @martinjrobins what do you think of the 2nd change? Is this a good idea in your opinion (the whole with block can be removed in that case, x64 is default too), or are we better off explicitly specifying the newest version we want to test on?

[codecov]

Codecov Report

Merging #1439 (f0276f2) into master (5b53eca) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master     #1439   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           90        90           
  Lines         8967      8971    +4     
=========================================
+ Hits          8967      8971    +4     

Impacted Files	Coverage Δ
pints/_evaluation.py	100.00% <0.00%> (ø)
pints/_mcmc/_nuts.py	100.00% <0.00%> (ø)
pints/_transformation.py	100.00% <0.00%> (ø)

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[MichaelClerx]

Only Python 3.11 to go now, and then we're on to Python 95!

[MichaelClerx]

Python for workgroups

[fcooper8472]

@MichaelClerx omitting the specific version appears to default to 3.x which means >=3.0.0 <4.0.0 so I think we would lose certainty about which version specifically is being tested on. That doesn't necessarily matter...

The other thing is we should change all actions/setup-python@v1 to actions/setup-python@v2 as there have been numerous enhancements to that functionality since we originally wrote our GitHub actions scripts.