Update actions/checkout requirement to v2.3.1

[dependabot]

⚠️ Dependabot is rebasing this PR ⚠️

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Updates the requirements on actions/checkout to permit the latest version.

Release notes

Sourced from actions/checkout's releases.

v2.3.1

Fix default branch resolution for .wiki and when using SSH

Changelog

Sourced from actions/checkout's changelog.

v2.3.1

• Fix default branch resolution for .wiki and when using SSH

v2.3.0

• Fallback to the default branch

v2.2.0

• Fetch all history for all tags and branches when fetch-depth=0

v2.1.1

• Changes to support GHES (here and here)

v2.1.0

• Group output
• Changes to support GHES alpha release
• Persist core.sshCommand for submodules
• Add support ssh
• Convert submodule SSH URL to HTTPS, when not using SSH
• Add submodule support
• Follow proxy settings
• Fix ref for pr closed event when a pr is merged
• Fix issue checking detached when git less than 2.22

v2.0.0

• Do not pass cred on command line
• Add input persist-credentials
• Fallback to REST API to download repo

v2 (beta)

• Improved fetch performance
  • The default behavior now fetches only the SHA being checked-out
• Script authenticated git commands
  • Persists with.token in the local git config
  • Enables your scripts to run authenticated git commands
  • Post-job cleanup removes the token
  • Coming soon: Opt out by setting with.persist-credentials to false
• Creates a local branch
  • No longer detached HEAD when checking out a branch
  • A local branch is created with the corresponding upstream branch set
• Improved layout
  • with.path is always relative to github.workspace
  • Aligns better with container actions, where github.workspace gets mapped in

Commits

• See full diff in compare view

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[codecov-commenter]

Codecov Report

Merging #14 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #14   +/-   ##
=======================================
  Coverage   99.68%   99.68%           
=======================================
  Files           5        5           
  Lines         320      320           
=======================================
  Hits          319      319           
  Misses          1        1           

Flag	Coverage Δ
#unittests	99.68% <ø> (ø)

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