For commits created by the new create-release.yml workflow, we can add
the corresponding release tag. This only runs for changes to the tag
JSON file (and the workflow itself) and only acts on changes created by
the automation (so that it won't interfere if we want to do things
manually).
The action runs the existing create_release.py script in a new mode
created for github actions. Rather than using local git commands, it
uses a public action for creating a PR in the repository. The action can
be triggered from the website or via the CLI tool, for example
gh workflow run create-release.yml -R emscripten-core/emsdk -F
lto-sha=abc123 -F nonlto-sha=234567