SUP-2343: remove "retry" example from "buildkite-agent step get" as not valid

[tomowatt]

Description

The "retry" attribute is not a valid for using with buildkite-agent step get command.

Context

Updating the docs on the buildkite-agent step commands to provide a list of valid attributes - see buildkite/docs#2872 - and ran the following, so see that "retry" is not a valid attribute for a Step:

$ buildkite-agent step get --format json
{
  "label": "label",
  "type": "command",
  "if": null,
  "state": "running",
  "key": "key",
  "outcome": null,
  "notify": [

  ],
  "command": "buildkite-agent step get --format json",
  "parallelism": null,
  "env": null,
  "timeout": 1,
  "concurrency_limit": null,
  "concurrency_key": null,
  "agents": null,
  "depends_on": [

  ]
}

and when running the following Pipeline:

steps:
  - label: "label"
    key: "key"
    command: buildkite-agent step get "retry" --format json
    retry: 
      automatic:
        signal_reason: "*"
        limit: 2

results in the following:

$ buildkite-agent step get "retry" --format json
2024-07-08 11:03:57 WARN   POST https://agent.buildkite.com/v3/steps/{STEP ID}/export: 400 Bad Request: `retry` is currently not supported. Please contact [email protected] if you'd like it added! (Attempt 1/10 Retrying in 5s)
fatal: failed to get step: POST https://agent.buildkite.com/v3/steps/{STEP ID}/export: 400 Bad Request: `retry` is currently not supported. Please contact [email protected] if you'd like it added!
🚨 Error: The command exited with status 1

Changes

Output changes

$ buildkite-agent step get --help                         
Usage:

    buildkite-agent step get <attribute> [options...]

Description:

Retrieve the value of an attribute in a step. If no attribute is passed, the
entire step will be returned.

In the event a complex object is returned (an object or an array),
you'll need to supply the --format option to tell the agent how it should
output the data (currently only JSON is supported).

Example:

    $ buildkite-agent step get "label" --step "key"
    $ buildkite-agent step get --format json
    $ buildkite-agent step get "state" --step "my-other-step"

Options:
...

Testing

• Tests have run locally (with go test ./...). Buildkite employees may check this if the pipeline has run automatically.
• Code is formatted (with go fmt ./...)

[DrJosh9000]

Good find!