Target older Kotlin stdlib to support Gradle 8.14

[vlsi]

Currently the plugin targets the latest kotlin stdlib, thus it yields the following error when org.checkerframework 1.0.2 applies with Gradle 8.14:

e: file:///home/runner/.gradle/caches/modules-2/files-2.1/org.checkerframework/checker-framework-gradle-plugin/1.0.2/d301b3076ef2f16810aa368d04fdbc88c497cbf9/checker-framework-gradle-plugin-1.0.2.jar!/META-INF/checker-framework-gradle-plugin.kotlin_module
Module was compiled with an incompatible version of Kotlin. The binary version of its metadata is 2.2.0, expected version is 2.0.0.

Please configure apiVersion, coreLibrariesVersion, languageVersion so the plugin is workable with older Gradle versions.
Targeting the latest one only makes it hard for the users to bump individual dependencies.

---

To put a concrete example:

• pgjdbc can't bump checkerframework plugin because it "requires" Gradle 9: fix(deps): update dependency org.checkerframework:org.checkerframework.gradle.plugin to v1 - autoclosed pgjdbc/pgjdbc#3976
• pgjdbc can't bump Gradle because checkerframework 0.6.61 does not support Gradle 9: chore(deps): update gradle to v9 - autoclosed pgjdbc/pgjdbc#3749

---

See also:

• Add a section on the importance of apiVersion, Xjdk-release, and java'c release Kotlin/api-guidelines#44