Revert auto-merged Roslyn bumps to restore package versions

[Copilot]

• Restore only Microsoft.CodeAnalysis.CSharp.Analyzer.Testing to 1.1.3 in src/StructId.Tests/StructId.Tests.csproj.
• Validate restore, build, existing tests, and formatting without changing other files; stop if newer APIs are required. Whitespace and git diff checks passed. Restore/build/style checks blocked by NU1301: https://pkg.kzu.app/index.json unavailable; targeted tests could not start. dnx --yes retest unavailable because dnx is not installed. API compatibility remains unverified; no code changes made.
• Scan the changed file, commit the one-line revert, and run automated review/security validation. No secrets or known dependency advisories found. Confirmed only one version attribute changed and working tree is clean. Automated validation invoked: code review unavailable in environment; CodeQL found no applicable code changes to analyze.

• Fixes Revert auto-merged Roslyn bumps (maintainer policy) #135

[kzu]

🧪 Details on Ubuntu 24.04.5 LTS

🧪 Details on macOS Unix 26.6.2

🧪 Details on Microsoft Windows 10.0.26100

from retest v1.1.0 on .NET 10.0.13 with 💜 by @devlooped