New GHA is caching test tasks, even though the JDK changes

[aSemy]

The test tasks aren't being re-run when the JDK changes. This might either be because Gradle thinks they're up to date, or because the JDK isn't changing (so the caching is correct).

https://github.com/stuebingerb/mockk/runs/8245418795?check_suite_focus=true#step:5:462

I'd be surprised if the JDK version wasn't registered as a task input by Gradle, but it's possible. It think it's more likely that the GHA isn't properly changing the JDK.

Originally found by @stuebingerb in #916 (comment)

Related #914

[stuebingerb]

I have disabled caching completely in https://github.com/stuebingerb/mockk/actions/runs/3014589035 and the tests still run fine. I believe it might be an issue with the jvm target not being set properly.

[stuebingerb]

I'm not sure if I have already fully understood the build, but to me it seems that the JVM toolchain uses it's values from Deps.Versions:

tasks.withType<JavaCompile>().configureEach {
    options.encoding = "UTF-8"
    sourceCompatibility = Deps.Versions.jvmTarget.toString()
    targetCompatibility = Deps.Versions.jvmTarget.toString()
}

tasks.withType<KotlinCompile>().configureEach {
    kotlinOptions {
        jvmTarget = Deps.Versions.jvmTarget.toString()
    }
}

And that seems to be hardcoded to JDK 8:

val jvmTarget = JavaVersion.VERSION_1_8

[stuebingerb]

There's also a javaToolchainMainVersion and a javaToolchainTestVersion but at first glance I only see the test version change in the matrix (which might be the reason for this error):

> Task :test-modules:performance-tests:compileKotlin FAILED
e: /home/runner/work/mockk/mockk/test-modules/performance-tests/src/main/kotlin/io/mockk/performance/JmhTest.kt: (27, 40): Cannot inline bytecode built with JVM target 11 into bytecode that is being built with JVM target 1.8. Please specify proper '-jvm-target' option