CHANGELOG.md was not updated after v1.86.0 release.

There is a [changelog generation workflow](https://github.com/googleapis/google-cloud-java/blob/main/.github/workflows/changelog_generation.yaml) that is supposed to split the release notes from main to CHANGELOG.md in each individual libraries.
However, it stopped working since monorepo migration. For example, [CHANGELOG.md](https://github.com/googleapis/google-cloud-java/blob/main/java-spanner/CHANGELOG.md ) in java-spanner was not updated after [v1.86.0 release](https://github.com/googleapis/google-cloud-java/releases/tag/v1.86.0).