fix: ParallelSteps child type so replacements happen correctly

[crenshaw-dev]

I failed to double-check the ParallelSteps child type in swagger.json and thus caused this: argoproj-labs/argo-client-gen#5

Tested make java in argo-client-gen. Still get a build error, but a different one (I don't think openapi-generator/java knows how to deal with nested lists). I'll open another issue for that one.

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this is a chore.
• The title of the PR is (a) conventional, (b) states what changed, and (c) suffixes the related issues number. E.g. "fix(controller): Updates such and such. Fixes #1234".
• I have written unit and/or e2e tests for my change. PRs without these are unlike to be merged.
• Optional. I've added My organization is added to the USERS.md.
• I've signed the CLA and required builds are green.

[codecov]

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  Branches          ?        0           
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  Hits              ?     3476           
  Misses            ?    26932           
  Partials          ?      470

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