Release candidate should be created even if updateChangelog does not return any new entries

[MajorLift]

Currently, the create-release-pr action is terminated with an error message ("updateChangelog" returned an empty value for package ...) and the release candidate is not created if the updateChangelog call does not return any new entries.

Presumably, the original intention for this behavior was to prevent a release candidate from being created if there are no new commits or changelog entries to be included in a new release.

However, the Wallet Framework Team is trialing a new practice of recording changelog entries under the "unreleased" heading. Because of this, all of the new commits may already have corresponding entries under the "unreleased" heading (which will have been migrated to the new release's heading by updateChangelog). This will result in a situation where there are new commits to be released, but updateChangelog still returns a null value.

Therefore, the error "updateChangelog" returned an empty value for package ... should be triggered only if both of the following are true:

• updateChangelog returns a null value.
• There are no unreleased changes present in the changelog.

The updateChangelog implementation @metamask/auto-changelog has a variable that could be used for this: hasUnreleasedChangesToRelease.