Cast to parent buffer for Java 8 buffer method compatibility

[jackshirazi]

What does this PR do?

Fixes java.lang.NoSuchMethodError: java.nio.ByteBuffer.clear()Ljava/nio/ByteBuffer;
at co.elastic.apm.agent.impl.context.BodyCaptureImpl$2.recycle(BodyCaptureImpl.java:44) ~[elastic-apm-agent-1.52.0.jar:1.52.0]
and similar

Checklist

• This is an enhancement of existing features, or a new feature in existing plugins
  • I have updated CHANGELOG.next-release.md
  • I have added tests that prove my fix is effective or that my feature works
  • Added an API method or config option? Document in which version this will be introduced
  • I have made corresponding changes to the documentation
• This is a bugfix
  • I have updated CHANGELOG.next-release.md
  • I have added tests that would fail without this fix
• This is a new plugin
  • I have updated CHANGELOG.next-release.md
  • My code follows the style guidelines of this project
  • I have made corresponding changes to the documentation
  • I have added tests that prove my fix is effective or that my feature works
  • New and existing unit tests pass locally with my changes
  • I have updated supported-technologies.md
  • Added an API method or config option? Document in which version this will be introduced
  • Added an instrumentation plugin? Describe how you made sure that old, non-supported versions are not instrumented by accident.
• This is something else
  • I have updated CHANGELOG.next-release.md

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