Chart releaser action does not detect changes when triggered by tag/release

[i5okie]

When chart-releaser action is run in a workflow triggered by a tag, or release, the action fails.
Chart-releaser fails to compare the file changes.

Example:

Run helm/chart-releaser-action@v1.5.0
Run owner=$(cut -d '/' -f 1 <<< "$GITHUB_REPOSITORY")
Looking up latest tag...
Discovering changed charts since 'v2.0.0-beta2'...
Nothing to do. No chart changes detected.

An existing issue exists: helm/chart-releaser-action#150
A PR exists with proposed changes that have not been approved/merged as of today: helm/chart-releaser-action#154

[esune]

Resolved by #343