Wheels in CI: Failing to set up Rust does not fail the "Running before_all" task

[matrixbot]

This issue has been migrated from #14136.

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See https://github.com/matrix-org/synapse/actions/runs/3226703547/jobs/5280558136

In this case, curl https://sh.rustup.rs/ -sSf | sh -s -- --default-toolchain stable -y failed because of a connectivity issue. However, since foo | bar succeeds if foo fails but bar succeeds, this isn't caught as a failure and the "Running before_all" tasks fails, leading to a more confusing error when building the wheels.

@DMRobertson says:

before-all = "bash -c 'set -o pipefail; curl https://sh.rustup.rs -sSf | sh -s -- --default-toolchain stable -y'" Might work? But is pretty write-only