bootstrap: Apply a clearer naming convention to many of the test steps

[Zalathar]

Hopefully this does a better job of helping contributors understand what each step does, at a glance.

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Original Zulip thread

[rustbot]

r? @Mark-Simulacrum

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[Zalathar]

@rustbot experimental
r? ghost

[rustbot]

Failed to set assignee to ghost: invalid assignee

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[onur-ozkan]

Please assign/ping me once it's ready.

[bors]

☔ The latest upstream changes (presumably #135086) made this pull request unmergeable. Please resolve the merge conflicts.