test: allow using global variables in suite-level variable definitions

[DanielMSchmidt]

This allows practitioners to define variables in .tfvar files, environment variables, CLI flags and use them in the definition of suit-level variables in the top-level variables block.

Fixes #34534
Fixes #34538

Target Release

1.8.x

Draft CHANGELOG entry

ENHANCEMENTS

• test: allow using global variables in suite-level variable definitions

[liamcervante]

Given that we do need to know about the type I don't know what I intended to say here.

[liamcervante]

Looks good! Just a couple of small things around naming and tidying up.

Generally a "TestSuite" refers to all the test files currently being executed not just the current test file, so there's a couple of places where I think we should change names and comments to reflect that.

Thanks!

[liamcervante]

Just a note on the changelog entry. I usually start with the full command, so something like:

• terraform test: File-level variables can now reference global variables.

Or something like that.

[github-actions]

Reminder for the merging maintainer: if this is a user-visible change, please update the changelog on the appropriate release branch.

[github-actions]

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