ValidatePlugins task now requires Java Toolchains

"In Gradle 9.0, using the ValidatePlugins task without applying
the Java Toolchains plugin will result in an error.

To fix this, explicitly apply the jvm-toolchains plugin."

Bug: 416235078
Test: N/A
Change-Id: Ibd90c9979b77445fa9389b1fb44bb65c608cb5fc