Switch `3.10-rc2` to `3.10` in GitHub Actions

[sobolevn]

We need to:

1. delete these lines https://github.com/dry-python/returns/blob/master/.github/workflows/test.yml#L21-L24
2. remove continue-on-error: https://github.com/dry-python/returns/blob/master/.github/workflows/test.yml#L17
3. add 3.10 here https://github.com/dry-python/returns/blob/master/.github/workflows/test.yml#L20

[jonbrohauge]

I'd like to do this