Remove usage of deprecated `org.gradle.util.VersionNumber`

[eskatos]

The deprecated VersionNumber type is used here:

gretty/libs/gretty/src/main/groovy/org/akhikhl/gretty/ServletContainerConfig.groovy

Line 16 in d25f2d3

import org.gradle.util.VersionNumber

We will add deprecation nagging in Gradle 8.5, see gradle/gradle#26776

[boris-petrov]

Thanks for letting us know! We'll for sure look into that before Gradle 9 is out.

[eskatos]

Gradle 9.0 is around the corner. This deprecated type will be removed and this plugin will stop working.