plz 17.1.0 build failure immediately causes all other builds in progress to fail

[robxu9]

On plz 17.0.0, when a build fails, existing builds that are still queued will still execute, meaning that the build will still try to proceed as much as possible before exiting:

[user@0a92eae9c511 workdir]$ plz --profile=rclone build //packages/meta-images/minimal-dev
Build stopped after 7m2.23s. 1 target failed:
    //third_party/c/chrony:git
Error building target //third_party/c/chrony:git: exit status 128
fatal: unable to access 'https://git.tuxfamily.org/chrony/chrony.git/': The requested URL returned error: 500

With plz 17.1.0, when a build fails, everything else immediately fails with "send on closed channel":

[user@0a92eae9c511 workdir]$ plz --profile=rclone build //packages/meta-images/minimal-dev
Build stopped after 22.16s. 344 targets failed:
    //third_party/c/chrony:git
Error building target //third_party/c/chrony:git: exit status 128                                                       
fatal: unable to access 'https://git.tuxfamily.org/chrony/chrony.git/': The requested URL returned error: 500

    //...
send on closed channel
    //...
send on closed channel
    //...
send on closed channel
    //...
send on closed channel
<repeats for another 340 or so times>

[stale[bot]]

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