_ci_: Run snap builds for lotus and lotus-filecoin in parallel

[ianconsolata]

This fixes a typo in my snapcraft config that causes it to fail after publishing the first snap but before building the second:
https://app.circleci.com/pipelines/github/filecoin-project/lotus/22519/workflows/7727083f-3fdf-45da-bb2d-ca2c7ff30d37/jobs/549504

While fixing it, I also tweaked it so we can run the two snap jobs in parallel. We still need to publish under both the new lotus snap name and the legacy lotus-filecoin snap name until all our users have migrated to the lotus one.

Checklist

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