[eas-cli] fix interpolated workflow URI validation

[davidmokos]

Why

A Slack workflow can read its webhook URL from an environment variable:

webhook_url: ${{ env.SLACK_WEBHOOK_URL }}

EAS CLI checks the workflow before it sends it to Expo's server. At that point, the environment variable has not been replaced with its real value. The local URL checker sees ${{ env.SLACK_WEBHOOK_URL }} instead of a URL and rejects the workflow.

Expo's server already accepts this workflow. The SDK does not validate Slack webhook URLs, so the bug is in EAS CLI's local check.

The EAS Workflows skill once had its own validator with the same problem. expo/skills#149 removed it and changed the skill to use eas workflow:validate. This PR fixes the check in EAS CLI instead of adding the validator back to the skill.

How

When a URI field contains ${{ ... }}, EAS CLI now waits for the workflow to resolve that value at runtime instead of trying to validate the unfinished URL.

Literal values still need to be valid URLs. For example, webhook_url: not a URL still fails validation. Other workflow and metadata checks do not change.

Fixes ENG-26025

Test Plan

• Added a test for ${{ env.SLACK_WEBHOOK_URL }}.
• Added a test that confirms an invalid literal URL still fails.
• Ran the EAS CLI tests and typecheck.
• Ran the repository lint and formatting checks.
• Checked the fix against the current production workflow schema.

[linear-code]

ENG-26025

[github-actions]

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File Patterns	Mentions
packages/eas-cli/**	@douglowder

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[codecov]

Codecov Report

❌ Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 65.51%. Comparing base (83fa42c) to head (617bc6f).

Files with missing lines	Patch %	Lines
...es/eas-cli/src/commandUtils/workflow/validation.ts	85.72%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4329      +/-   ##
==========================================
+ Coverage   65.48%   65.51%   +0.04%     
==========================================
  Files        1060     1060              
  Lines       49302    49305       +3     
  Branches    10437    10438       +1     
==========================================
+ Hits        32282    32299      +17     
+ Misses      16904    16890      -14     
  Partials      116      116              

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[github-actions]

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