Migrate to release-please-action@v4

[fapspirit]

This PR is to migrate to release-please-action@v4.

This is to address the following warning from the release job (example):

Warning: Unexpected input(s) 'package-name', 'command', valid inputs are ['token', 'release-type', 'path', 'target-branch', 'config-file', 'manifest-file', 'repo-url', 'github-api-url', 'github-graphql-url', 'fork', 'include-component-in-tag', 'proxy-server', 'skip-github-release', 'skip-github-pull-request', 'skip-labeling', 'changelog-host']

I've followed this migration guide: https://github.com/googleapis/release-please-action?tab=readme-ov-file#upgrading-from-v3-to-v4

This change should help unblocking #470