fix: ci: publish correct docker tags on workflow dispatch

[galargh]

Related Issues

https://ipdx-workspace.slack.com/archives/CP50PPW2X/p1716967567670129

Proposed Changes

When the workflow is triggered manually, infer the sha and ref to use for generating Docker metadata from the git checkout instead of relying on the github context (which points to the git info of the version of the workflow we're using).

Additional Info

We didn't release the tag before because the tag release was tied to the tag push trigger only. I have now run the workflow again (from this branch) and verified the tag is being correctly pushed:

• https://github.com/filecoin-project/lotus/actions/runs/9283617669/job/25544197664
• e.g. https://hub.docker.com/layers/filecoin/lotus-all-in-one/v1.27.0/images/sha256-975685469d3785934d767d97c3a4a7275a273fdd1fe0a73ebdc51e7a9bf032bd?context=explore

Checklist

Before you mark the PR ready for review, please make sure that:

• Commits have a clear commit message.
• PR title is in the form of of <PR type>: <area>: <change being made>
  • example: fix: mempool: Introduce a cache for valid signatures
  • PR type: fix, feat, build, chore, ci, docs, perf, refactor, revert, style, test
  • area, e.g. api, chain, state, market, mempool, multisig, networking, paych, proving, sealing, wallet, deps
• If the PR affects users (e.g., new feature, bug fix, system requirements change), update the CHANGELOG.md and add details to the UNRELEASED section.
• New features have usage guidelines and / or documentation updates in
  • Lotus Documentation
  • Discussion Tutorials
• Tests exist for new functionality or change in behavior
• CI is green

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