Build action does not pass platform through

[aelkiss]

Build workflow takes a platform parameter (https://github.com/hathitrust/actions_playground/blob/main/.github/workflows/build.yml#L16-L23) but does not pass that through to the underlying hathitrust/github_actions/build action.

[aelkiss]

I noticed this when attempting to build post-zephir processing; I specified the amd64 platform but it kept doing arm stuff and taking forever (https://github.com/hathitrust/post_zephir_processing/actions/runs/11673208678)