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

This issue has been migrated from [#14136](https://github.com/matrix-org/synapse/issues/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](https://matrix.to/#/!vcyiEtMVHIhWXcJAfl:sw1v.org/$aT_PAugIrgLMGObZrako-0IksSzcz6IoGJ-xRvPCB5g?via=matrix.org&via=element.io&via=beeper.com):

> `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