nexus: allow instance updates to complete when one switch is down - #10389

control: job assigned to worker 01KR1Q69JGP7SWVH8ASTV152JS [factory aws, i-01cc2b1fef7f4a7e4] (queued for 55 s)
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task: starting task 0: "setup"
task: process exited: duration 3161 ms, exit code 0
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task: starting task 1: "rust-toolchain"
task: process exited: duration 17331 ms, exit code 0
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task: starting task 2: "authentication"
task: process exited: duration 15 ms, exit code 0
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task: starting task 3: "clone repository"
task: process exited: duration 11013 ms, exit code 0
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task: starting task 4: "build"
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|    Compiling protocol v0.1.0 (https://github.com/oxidecomputer/lldp#d22509df)
|    Compiling parse-display v0.10.0
|    Compiling serde_with v3.17.0
|    Compiling tufaceous-artifact v0.1.0 (https://github.com/oxidecomputer/tufaceous?branch= [...]
|    Compiling api_identity v0.1.0 (/work/oxidecomputer/omicron/api_identity)
|    Compiling omicron-ledger v0.1.0 (/work/oxidecomputer/omicron/ledger)
|    Compiling regress v0.10.5
|    Compiling macaddr v1.0.1
|    Compiling rustls-webpki v0.103.9
|    Compiling tokio-rustls v0.26.4
|    Compiling rustls-platform-verifier v0.6.2
|    Compiling hyper-rustls v0.27.7
|    Compiling reqwest v0.13.2
|    Compiling progenitor-client v0.14.0
|    Compiling progenitor-extras v0.2.0
|    Compiling omicron-common v0.1.0 (/work/oxidecomputer/omicron/common)
|    Compiling test-project v0.1.0 (/tmp/test-project)
|     Finished `release` profile [optimized] target(s) in 1m 12s
task: process exited: duration 113911 ms, exit code 0
|W| found 0 output files