BlockHound and debug agent tests use toolchains

[chemicL]

Running BlockHound and debug agent tests using JDK greater than 8 would fail due to improper version checks. JavaVersion.current() reports the JDK used to run gradle, while we are interested in the JDK currently in use by the current toolchain.

[violetagg]

openjdk version "21.0.5" 2024-10-15 LTS
OpenJDK Runtime Environment Corretto-21.0.5.11.1 (build 21.0.5+11-LTS)
OpenJDK 64-Bit Server VM Corretto-21.0.5.11.1 (build 21.0.5+11-LTS, mixed mode, sharing)

./gradlew publishToMavenLocal

* Where:
Build file '/.../reactor-core/reactor-tools/build.gradle' line: 140

* What went wrong:
A problem occurred configuring project ':reactor-tools'.
> Could not resolve all dependencies for configuration ':reactor-tools:compileClasspath'.
   > Failed to calculate the value of task ':reactor-core:compileJava9Java' property 'javaCompiler'.
      > No matching toolchains found for requested specification: {languageVersion=9, vendor=any, implementation=vendor-specific} for MAC_OS on aarch64.
         > No locally installed toolchains match and the configured toolchain download repositories aren't able to provide a match either.

[chemicL]

Yep, that's expected: https://github.com/reactor/reactor-core?tab=readme-ov-file#trouble-building-the-project