skip build if commit message contains "[skip ci]"

Revert "Use JDK 18 GA instead of 18 EA"

Temurin 18 is not yet released for all platform.
Revert to the EA version until the GA version
is available for all platforms.

This reverts commit aa88e4e.

Use JDK 18 GA instead of 18 EA

JDK 18 is now released, use the GA version instead
of EA in build matrix.

Add JDK 18 early-access build to Maven build matrix

18 is the upcoming version of JDK so it is nice
to verify all Plexus components work with it.

Add JDK 18 early-access build to Maven build matrix

18 is the upcoming version of JDK so it is nice
to verify all Plexus components work with it.

fix string

Signed-off-by: Olivier Lamy <[email protected]>