Allow env_var to be Used in More Contexts

[peterallenwebb]

Resolves #10599

Problem

Solution

Checklist

• I have read the contributing guide and understand what's expected of me.
• I have run this code in development, and it appears to resolve the stated issue.
• This PR includes tests, or tests are not required or relevant for this PR.
• This PR has no interface changes (e.g., macros, CLI, logs, JSON artifacts, config files, adapter interface, etc.) or this PR has already received feedback and approval from Product or DX.
• This PR includes type annotations for new and modified functions.

[github-actions]

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[peterallenwebb]

@gshank Can you take a look at this proposed change? I found that this happens because a MacroManifest was showing up in the implementation of env_var(), when we were only expecting a Manifest. I improved the type annotations so that they better reflect reality, but that did require adding some assertions.

Do you think partial parsing will work correctly with these changes?

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Project coverage is 86.20%. Comparing base (3c55806) to head (566e294).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10601      +/-   ##
==========================================
- Coverage   88.90%   86.20%   -2.70%     
==========================================
  Files         180      180              
  Lines       22760    22764       +4     
==========================================
- Hits        20234    19623     -611     
- Misses       2526     3141     +615     

Flag	Coverage Δ
integration	86.20% <85.71%> (+0.05%)	⬆️
unit	?

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Components	Coverage Δ
Unit Tests	86.20% <85.71%> (-2.70%)	⬇️
Integration Tests	86.20% <85.71%> (+0.05%)	⬆️