Bump cia.project.versions.vaadin from 8.12-SNAPSHOT to 8.12.0.alpha1
Bump cia.project.versions.vaadin from 8.12-SNAPSHOT to 8.12.0.alpha1

Bumps `cia.project.versions.vaadin` from 8.12-SNAPSHOT to 8.12.0.alpha1.

Updates `vaadin-themes` from 8.12-SNAPSHOT to 8.12.0.alpha1
- [Release notes](https://github.com/vaadin/framework/releases)
- [Commits](https://github.com/vaadin/framework/commits/8.12.0.alpha1)

Updates `vaadin-compatibility-server` from 8.12-SNAPSHOT to 8.12.0.alpha1
- [Release notes](https://github.com/vaadin/framework/releases)
- [Commits](https://github.com/vaadin/framework/commits/8.12.0.alpha1)

Updates `vaadin-maven-plugin` from 8.12-SNAPSHOT to 8.12.0.alpha1
- [Release notes](https://github.com/vaadin/maven-plugin/releases)
- [Commits](https://github.com/vaadin/maven-plugin/commits/8.12.0.alpha1)

Signed-off-by: dependabot-preview[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
Hack23/cia,Hack23/cia,Hack23/cia,Hack23/cia