terraform test: fix crash when non-applyable plans are applied

[liamcervante]

This fixes a crash in 1.11 branch that occurs when a run block in a test file fails due to a non-applyable plan. It later tries to deference the null state and crashes. This was already fixed in main during a larger refactor in which the actual crash wasn't detected, so I'm pushing directly to 1.11.

We shouldn't merge this until after the 1.11.0 release happens later this week, with the target release for this PR being 1.11.1 next week.

I will forward port the test that was added here so we don't accidentally cause a regression in main.

Fixes #

Target Release

1.11.1

CHANGELOG entry

• This change is user-facing and I added a changelog entry.
• This change is not user-facing.

[github-actions]

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