Summary of PR changes

Updating the action so we don't provide a default commitish value. It's led to confusion and things not being tagged appropriately depending on how items were merged so we'll leave it up to the user to decide what should be tagged.

PR Requirements

[x] For JavaScript actions, the action has been recompiled.
- See the Recompiling section of the repository's README.md for more details.
- This does not apply to Composite Run Steps actions unless a package.json is present and contains a build script.
[x] For major, minor, or breaking changes, at least one of the commit messages contains the appropriate +semver: keywords.
- See the Incrementing the Version section of the repository's README.md for more details.
[x] The examples in the repository's README.md have been updated with the new version.
- See the Incrementing the Version section of the repository's README.md for more details on how the version will be incremented.
[x] The action code does not contain sensitive information.