Update actions/checkout in GitHub Actions workflows to v3

[striezel]

Updates the actions/checkout action used in the GitHub Actions workflows to its newest major version.

Changes in actions/checkout:

v3.5.2

• Fix api endpoint for GHES

v3.5.1

• Fix slow checkout on Windows

v3.5.0

• Add new public key for known_hosts

v3.4.0

• Upgrade codeql actions to v2
• Upgrade dependencies
• Upgrade @actions/io

v3.3.0

• Implement branch list using callbacks from exec function
• Add in explicit reference to private checkout options
• Fix comment typos

v3.2.0

• Add GitHub Action to perform release
• Fix status badge
• Replace datadog/squid with ubuntu/squid Docker image
• Wrap pipeline commands for submoduleForeach in quotes
• Update @actions/io to 1.1.2
• Upgrading version to 3.2.0

v3.1.0

• Use @actions/core saveState and getState
• Add github-server-url input

v3.0.2

• Add input set-safe-directory

v3.0.1

• Fixed an issue where checkout failed to run in container jobs due to the new git setting safe.directory
• Bumped various npm package versions

v3.0.0

• Update to node 16

[striezel]

@althonos: I've rebased the changes to solve the merge conflicts.

[striezel]

Looks like a part of those changes were made in c7c77f0 an hour ago. Should I rebase this again? (It still can be merged without conflicts, so strictly speaking it is not necessary to rebase the pull request.)

[althonos]

Thanks, this should be fine, I will squash the commit so no need to rebase.