Bump plexapi from 4.15.13 to 4.15.15 (#1478)

Bump plexapi from 4.15.13 to 4.15.15 (#1478)

* Bump plexapi from 4.15.13 to 4.15.15

Bumps [plexapi](https://github.com/pkkid/python-plexapi) from 4.15.13 to 4.15.15.
- [Release notes](https://github.com/pkkid/python-plexapi/releases)
- [Commits](https://github.com/pkkid/python-plexapi/compare/4.15.13...4.15.15)

---
updated-dependencies:
- dependency-name: plexapi
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
* Update manifest.json

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Marcel van der Veldt <m.vanderveldt@outlook.com>