configure ci for python 3.10

[graingert-coef]

Fixes #1863

switch 3.9 CI to 3.10 CI

Contributor Checklist

• I have broken down my PR scope into the following TODO tasks
  • change ci to use python 3.10
• I have run the tests locally and they passed. (refer to testing section in contributing)
• I have added tests, or extended existing tests, to cover any new features or bugs fixed in this PR

optionals

• I have added entry in the CHANGELOG.md
• If this PR needs a follow-up in dash docs, community thread, I have mentioned the relevant URLS as follows
  • this GitHub #PR number updates the dash docs
  • here is the show and tell thread in Plotly Dash community

[graingert-coef]

So CI passed on 3.10 for everything except "Display npm errors and exit on failed builds". Locally running "npm ci" always writes logs so I don't see how to make this step pass

[graingert]

since npm/cli@6734ba3 (npm v8.2) npm will always write debug logs

[alexcjohnson]

Let's take the Python version number off of the Percy snapshots - no reason they should all look brand new just because we changed that, and we've long since stopped taking snapshots on multiple Python versions.

That's here:

dash/dash/testing/browser.py

Line 162 in 6a8da52

snapshot_name = f"{name} - py{sys.version_info.major}.{sys.version_info.minor}"

[alexcjohnson]

So CI passed on 3.10 for everything except "Display npm errors and exit on failed builds". Locally running "npm ci" always writes logs so I don't see how to make this step pass

Good to know! These still may be useful for debugging when tests DO fail - so perhaps we can either keep the cat in that step, just don't have it cause a failure, or copy those logs to the test artifacts?

[alexcjohnson]

Ah that's a good strategy - this means we know what changes if any the rest of the changes in this PR cause in the percy snapshots. After merging we can make another PR to remove the version number entirely, which will cause all the snapshots to look new but we can blindly approve.

[alexcjohnson]

💃 Great work, thanks!