More accurate error messages when setting target release after mupdate - #11018

control: job assigned to worker 01KZ9P5B8JJ24AWYYV6T9EKC02 [factory aws, i-0abc1250aebca0446] (queued for 52 s)
...
task: starting task 0: "setup"
task: process exited: duration 4125 ms, exit code 0
...
task: starting task 1: "rust-toolchain"
task: process exited: duration 17313 ms, exit code 0
...
task: starting task 2: "authentication"
task: process exited: duration 23 ms, exit code 0
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task: starting task 3: "clone repository"
task: process exited: duration 18635 ms, exit code 0
...
task: starting task 4: "build"
...
| + unset TMPDIR
| + echo 'files in /var/tmp/omicron_tmp (none expected on success):'
| files in /var/tmp/omicron_tmp (none expected on success):
| + find /var/tmp/omicron_tmp -ls
| 135196   32 drwxr-xr-x   2 build    build           2 Aug  5 19:58 /var/tmp/omicron_tmp
| + rmdir /var/tmp/omicron_tmp
task: process exited: duration 1953743 ms, exit code 0
|W| found 6 output files
|W| uploading: /work/cargo-build-analysis.jsonl (1803251 bytes)
|W| uploaded: /work/cargo-build-analysis.jsonl
|W| uploading: /work/environment.json (108 bytes)
|W| uploaded: /work/environment.json
|W| uploading: /work/oxidecomputer/omicron/target/nextest/ci/junit.xml (645191 bytes)
|W| uploaded: /work/oxidecomputer/omicron/target/nextest/ci/junit.xml
|W| uploading: /work/oxidecomputer/omicron/target/live-tests-archive.tgz (280506880 bytes)
|W| uploaded: /work/oxidecomputer/omicron/target/live-tests-archive.tgz
|W| uploading: /tmp/nextest-run-archive.zip (3139150 bytes)
|W| uploaded: /tmp/nextest-run-archive.zip
|W| uploading: /tmp/nextest-chrome-trace.json (4109440 bytes)
|W| uploaded: /tmp/nextest-chrome-trace.json