Update GitHub Action steps to use Node 16

[zimeg]

Summary

This PR bumps the versions of the actions/checkout and actions/setup-python actions to the latest versions to remove the warning of using a deprecated Node version in GitHub Actions.

I am hoping that this might fix the unresolved "Waiting for status to be reported" status from the codecov step too 👀

Category

• slack_sdk.web.WebClient (sync/async) (Web API client)
• slack_sdk.webhook.WebhookClient (sync/async) (Incoming Webhook, response_url sender)
• slack_sdk.socket_mode (Socket Mode client)
• slack_sdk.signature (Request Signature Verifier)
• slack_sdk.oauth (OAuth Flow Utilities)
• slack_sdk.models (UI component builders)
• slack_sdk.scim (SCIM API client)
• slack_sdk.audit_logs (Audit Logs API client)
• slack_sdk.rtm_v2 (RTM client)
• /docs-src (Documents, have you run ./scripts/docs.sh?)
• /docs-src-v2 (Documents, have you run ./scripts/docs-v2.sh?)
• /tutorial (PythOnBoardingBot tutorial)
• tests/integration_tests (Automated tests for this library)

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've run python3 -m venv .venv && source .venv/bin/activate && ./scripts/run_validation.sh after making the changes.

[codecov]

Codecov Report

Merging #1375 (7112eb0) into main (3afc31a) will not change coverage.
The diff coverage is n/a.

❗ Current head 7112eb0 differs from pull request most recent head 09bae2c. Consider uploading reports for the commit 09bae2c to get more accurate results

@@           Coverage Diff           @@
##             main    #1375   +/-   ##
=======================================
  Coverage   85.55%   85.55%           
=======================================
  Files         111      111           
  Lines       11570    11570           
=======================================
  Hits         9899     9899           
  Misses       1671     1671           

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[seratch]

Thanks!