All extension network traffic breaks when system proxy settings are changed

<!-- ⚠️⚠️ Do Not Delete This! bug_report_template ⚠️⚠️ --> <!-- Please read our Rules of Conduct: https://opensource.microsoft.com/codeofconduct/ --> <!-- 🕮 Read our guide about submitting issues: https://github.com/microsoft/vscode/wiki/Submitting-Bugs-and-Suggestions --> <!-- 🔎 Search existing issues to avoid creating duplicates. --> <!-- 🧪 Test using the latest Insiders build to see if your issue has already been fixed: https://code.visualstudio.com/insiders/ --> <!-- 💡 Instead of creating your report here, use 'Report Issue' from the 'Help' menu in VS Code to pre-fill useful information. --> <!-- 🔧 Launch with `code --disable-extensions` to check. --> Does this issue occur when all extensions are disabled?: No -- this is a bug that affects all extensions - VS Code Version: 1.75.1 - OS Version: macOS Monterey 12.5.1 Steps to Reproduce: 1. Close VSCode 2. Set a system-level proxy (I do this by running Proxyman) 3. Start VSCode -- note, all VSCode extension traffic correctly goes through the proxy 4. Change the proxy settings (in this case, close Proxyman) 5. All VSCode extension traffic stops working. It looks like all traffic continues to be routed through the proxy even though the proxy is no longer active. This appears to affect *all* extensions. I see this behaviour with our own extension (using `node-fetch`) but also in the GitHub extension. The error I see in the GitHub extension is `Fetching pull requests failed: request to https://api.github.com/repos/matthewjamesadam/vscode/pulls?per_page=20&page=1 failed, reason: connect ECONNREFUSED 127.0.0.1:9090`. <img width="450" alt="Screen Shot 2023-02-13 at 11 30 19 AM" src="https://user-images.githubusercontent.com/2133518/218558166-be3d6d23-814a-4ce2-b664-c39597785b97.png"> Note that built-in VSCode network traffic continues to work -- in the extension sidebar I can search the marketplace, for instance. So this seems to be something particular to extension network traffic. I am willing to look into fixi…