The file github_update_release.txt contains the name of GitHub release (Git tag)
where the current release should be uploaded.
This is only relevant for CGE master branch.

Example values:
- "snapshot" ( https://github.com/castle-engine/castle-engine/releases/tag/snapshot )
- "v7.0-alpha.2" ( https://github.com/castle-engine/castle-engine/releases/tag/v7.0-alpha.2 )

The github_update_release.txt file can have a newline after the release name.
Other than that, it cannot contain any extra comments or whitespace.

If github_update_release.txt is empty, this commit is not uploaded as any GitHub release.

Note: The Jenkins job that uploads GitHub releases is hosted outside of CGE repo,
for security (it needs to use GitHub token with write permissions,
so only CGE admins should have ability to interact with it).
