Fix spurious failures in the ssh_identities test - #35

control: job assigned to worker 01KZRPTKTDMQKGFTVHZWGG1Y4S [factory aws, i-01d3bb3e5df2916ac] (queued for 45 s)
...
task: starting task 0: "setup"
task: process exited: duration 4110 ms, exit code 0
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task: starting task 1: "rust-toolchain"
task: process exited: duration 16243 ms, exit code 0
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task: starting task 2: "authentication"
task: process exited: duration 16 ms, exit code 0
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task: starting task 3: "clone repository"
task: process exited: duration 1034 ms, exit code 0
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task: starting task 4: "build"
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|    Compiling unicode-segmentation v1.12.0
|    Compiling home v0.5.12
|    Compiling xdg v2.5.2
|    Compiling natord v1.0.9
|    Compiling unit-prefix v0.5.2
|    Compiling permission-slip-client v1.1.0 (https://github.com/oxidecomputer/permission-sl [...]
|    Compiling indicatif v0.18.3
|    Compiling rustyline v17.0.2
|    Compiling sush-api v0.1.0 (/work/oxidecomputer/sush/api)
|    Compiling tokio-fd v0.3.0
|    Compiling async-recursion v1.1.1
|    Compiling xdg v3.0.0
|    Compiling humantime v2.3.0
|    Compiling sush-client v0.1.0 (/work/oxidecomputer/sush/client)
|     Finished `release` profile [optimized] target(s) in 1m 44s
| + cp target/release/sush /work/sush
task: process exited: duration 105341 ms, exit code 0
|W| found 1 output files
|W| uploading: /work/sush (34122488 bytes)
|W| uploaded: /work/sush