Update build.yaml to use setup-python v4

[LucaMarconato]

Using setup-python v4 with pip caching. It should run noticeably faster, let's see.

We may need to upload a second commit to see the caching mechanism in action.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 92.54%. Comparing base (1f74e77) to head (b84423f).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #509 +/- ## ======================================= Coverage 92.54% 92.54% ======================================= Files 43 43 Lines 5969 5969 ======================================= Hits 5524 5524 Misses 445 445 ```

[LucaMarconato]

Some stats on the runtimes. Running tests takes around 3-4. I see a lot of variability on the installation of packages (the run that lasted 25min was 22min of packages installation).

• checkout v4, second run (first run)

  • 3.9, ubuntu-latest: XXX
  • 3.10, ubuntu-latest: XXX
  • 3.9, macos: XXX
  • 3.10, --pre, macos: XXX

• checkout v4, second run (caching in action)

  • 3.9, ubuntu-latest: XXX
  • 3.10, ubuntu-latest: XXX
  • 3.9, macos: XXX
  • 3.10, --pre, macos: XXX

• checkout v2, first replicated

  • 3.9, ubuntu-latest: 8m
  • 3.10, ubuntu-latest: 8m
  • 3.9, macos: 7m
  • 3.10, --pre, macos: 11m

• checkout v2, second replicate

  • 3.9, ubuntu-latest: 7m
  • 3.10, ubuntu-latest: 7m
  • 3.9, macos: 13m
  • 3.10, --pre, macos: 7m

• checkout v2, third replicate

  • 3.9, ubuntu-latest: 25m
  • 3.10, ubuntu-latest: 8m
  • 3.9, macos: 8m
  • 3.10, --pre, macos: 6m

[LucaMarconato]

I had modified this on build.yaml, not on test_and_deploy.yaml. Now it's fixed.

[LucaMarconato]

Installing the dependencies seems to be a bit faster, but not consistently faster. Let's this out.