The action was previously working fine (see this build which was built against glektarssza/webcraft@05cd8fedb7f03b07587ad79f1fe599f155b38f04).
As you can see from the above mentioned build/commit combination, the project has a package.json with a packageManager field.
I went to update pnpm this morning and the build has randomly started failing. See this build, the commit it was built against, and the package.json in that commit which has a packageManager field in the same format.
This is unexpected and confusing behaviour and quite likely a bug.