Bump com.github.siom79.japicmp:japicmp-maven-plugin (#2615)

Bumps [com.github.siom79.japicmp:japicmp-maven-plugin](https://github.com/siom79/japicmp) from 0.25.4 to 0.25.6.
- [Release notes](https://github.com/siom79/japicmp/releases)
- [Changelog](https://github.com/siom79/japicmp/blob/master/release.py)
- [Commits](https://github.com/siom79/japicmp/compare/japicmp-base-0.25.4...japicmp-base-0.25.6)

---
updated-dependencies:
- dependency-name: com.github.siom79.japicmp:japicmp-maven-plugin
  dependency-version: 0.25.6
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>