Bundle releases include pre-release library releases

The automatic bundle releases made by @adafruit-adabot include releases of libraries marked as `pre-release`. I suggest releases of the bundle marked as `stable` should only include stable library releases.

Library `pre-release` releases could either be ignored entirely or @adafruit-adabot could make `pre-release` releases of the bundle which include pre-releases of libraries.

If @adafruit-adabot can't differentiate `pre-release` from `stable` releases via GitHub's Releases, it could treat any tags on non-default branches as pre-releases.