Allow id-token: write permission in strict mode

[Copilot]

The id-token: write permission enables OIDC token generation for cloud provider authentication (AWS, GCP, Azure) and doesn't modify repository content, making it safe for strict mode.

Changes

• Excluded id-token from dangerous permissions validator in findWritePermissions() - it now skips PermissionIdToken when checking for write permissions that require the feature flag
• Added test coverage for id-token: write behavior in both general and strict modes
• Fixed pre-existing test bugs: removed invalid "write" shorthand test (not a valid GitHub Actions shorthand), corrected MCP container network validation test expectations

Example

Workflows can now use id-token: write in strict mode for OIDC authentication:

---
name: Deploy to AWS
on: push
strict: true
permissions:
  id-token: write      # Now allowed - used for AWS authentication
  contents: read
---

This continues to block repository-modifying permissions like contents: write, issues: write, and pull-requests: write in strict mode.

Original prompt

Allow idtoken: write permission in strict mode.

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