chore(main): release 2.5.6-SNAPSHOT (#741)

:robot: I have created a release *beep* *boop*
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### Updating meta-information for bleeding-edge SNAPSHOT release.

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This PR was generated with [Release Please](https://github.com/googleapis/release-please). See [documentation](https://github.com/googleapis/release-please#release-please).
7 files changed
tree: 5ae9b82407887c93211a3119c7c1665344ecc4f5
  1. java-core/