Work around broken github/runner input handling for post steps

[jsoref]

Address #2553 until the underlying github/runner is fixed everywhere (including GHES which is over a year from now).

Merge / deployment checklist

• Confirm this change is backwards compatible with existing workflows. -- State is supposed to be stored on a per action basis, so barring other bugs in github/runner, this change should do the right thing.
• Confirm the readme has been updated if necessary. -- This is really a bug fix that users shouldn't care about
• Confirm the changelog has been updated if necessary. -- I've added an entry since it's where I'd look (other than just searching /issues/) for such a thing when I trip over it and am wondering if it's been "fixed".

[jsoref]

Closing in favor of #2557