Enable immutable releases on this project

This action should enable [immutable releases](https://docs.github.com/en/code-security/concepts/supply-chain-security/immutable-releases) to help protect users against potential attacks such as GHSA-mrrh-fwg8-r2c3 and GHSA-69fq-xp46-6x23 by preventing re-pointing (released) tags to different commits.

Start with the release-please-action entry point and read the linked GitHub immutable releases documentation. Determine whether this request belongs in the action or in project configuration, then verify that released tags cannot be re-pointed to different commits. Done means releases created by this project are protected from the referenced tag-changing attacks.

Written by the indexing model from the issue text.