CI: Override JetBrains toolchain vendor for Nix JDK compatibility
The gradle-daemon-jvm.properties requires JetBrains JDK which isn't
available in CI. Patch to ADOPTIUM at build time and set JAVA_HOME
explicitly to the Nix-provided JDK.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>