docs: Add a release note for JDK 15 support.
### Resolved issues
* (IDETECT-2434) Resolved an issue in the CLANG detector on Ubuntu and Debian systems that caused it to omit a package when that package had been installed on the system from multiple architectures.
* (IDETECT-2409) Resolved an issue in the Gradle Inspector to support Gradle 6.8.
+* (IDETECT-2413) Resolved an issue to upgrade internal dependencies to support JDK 15.
## Version 6.9.0
### New Features
