Remove usage of deprecated org.gradle.api.Project.javaexec

[mlopatkin]

This method is being deprecated in Gradle 8.11 with the intention to remove it in Gradle 9.

The deprecated method is used here:

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

Line 84 in 5b99776

project.javaexec { JavaExecSpec spec ->

Gradle will add deprecation nagging in gradle/gradle#30512.

From a cursory glance, ExecOperations should be a good replacement and will help to eventually adopt the configuration cache.

[boris-petrov]

Thanks for the heads-up! PRs are more than welcome. For this deprecation and for the other one.