JMH Gradle plugin 0.7.3

[greg-at-moderne]

What's changed?

Upgrading the JMH Gradle plugin to the latest available version (0.7.3).

What's your motivation?

• It started with me seeing a Space-assignment syntax in Groovy DSL has been deprecated. warning in an unrelated Gradle build
• then I noticed we are using an old version, and the old version is violating the minimal plugin version as per https://github.com/melix/jmh-gradle-plugin/blob/493a4f0ca583d95ee5a61f20ae840d8d83eaa108/README.adoc#L38
• and then I tried running the JMH benchmarks locally and without the change they failed with the following error (which goes away after the upgrade):

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':rewrite-benchmarks:jmhRunBytecodeGenerator'.
> 'void org.gradle.workers.WorkerExecutor.submit(java.lang.Class, org.gradle.api.Action)'