Update cgmanifest to match CMakeLists.txt

[OneBlue]

Summary of the Pull Request

This change updates cgmanifest.json to match our current dependencies in CMakeLists.txt

PR Checklist

• Closes: Link to issue #xxx
• Communication: I've discussed this with core contributors already. If work hasn't been agreed, this work might be rejected
• Tests: Added/updated if needed and all pass
• Localization: All end user facing strings can be localized
• Dev docs: Added/updated if needed
• Documentation updated: If checked, please file a pull request on our docs repo and link it here: #xxx

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

[Copilot]

Pull request overview

This PR updates the component governance manifest (cgmanifest.json) to reflect the current CMake FetchContent-downloaded dependencies, and adds a reminder in CMakeLists.txt to keep the manifest in sync.

Changes:

• Remove the prior git-based GSL registration from cgmanifest.json.
• Add other registrations in cgmanifest.json for GSL v4.0.0 and nlohmann/json v3.12.0 (matching the CMake URLs/hashes).
• Add a CMake note indicating dependency changes should be reflected in cgmanifest.json.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
cgmanifest.json	Updates governance registrations to include the current tarball-based FetchContent dependencies (GSL, nlohmann/json).
CMakeLists.txt	Adds a reminder comment to keep cgmanifest.json aligned with the FetchContent dependency declarations.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.