## Summary
- Windows release builds fail during code signing because the Azure
Trusted Signing DLL cannot parse the signing metadata JSON file
- The `signing-metadata.json` is written with a UTF-8 BOM (0xEF 0xBB
0xBF) by Windows PowerShell 5.1's `Out-File -Encoding utf8`, and .NET's
`System.Text.Json` parser rejects the BOM as invalid JSON
- Fix: switch `shell: powershell` to `shell: pwsh` (PowerShell Core)
which writes UTF-8 without BOM by default

## Test plan
- Re-run the release workflow and verify the Windows build completes
signing successfully

#skip-bugbot

🤖 Generated with [Claude Code](https://claude.com/claude-code)
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<!-- This is an auto-generated description by cubic. -->
---
## Summary by cubic
Fix Windows release signing failures by switching the workflow to
PowerShell Core (pwsh) so signing-metadata.json is written as UTF-8
without a BOM. This avoids the .NET System.Text.Json BOM error and lets
Azure Trusted Signing parse the file successfully.

<sup>Written for commit b1967255ec4547681dd5650fe0c2154b7374f0ad.
Summary will update on new commits.</sup>

<!-- End of auto-generated description by cubic. -->
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>