Does this issue occur when all extensions are disabled?: N/a

• VS Code Version:
• Version: 1.72.0
  Commit: Unknown
  Date: Unknown
  Electron: 19.0.17
  Chromium: 102.0.5005.167
  Node.js: 16.14.2
  V8: 10.2.154.15-electron.0
  OS: Windows_NT x64 10.0.19044
  Sandboxed: No

Steps to Reproduce:

1. Compile the test-provider-sample at https://github.com/microsoft/vscode-extension-samples/compare/main...r3m0t:vscode-extension-samples:test-eg-mutable-tags?expand=1 which just adds a command "Banana" that assigns to TestItem.tags on all tests.
2. Run the sample and open the example folder with the .md files. Test cases appear.
3. Run Banana to add the initial tags. Enter the filter @mathTestController:mytag
4. Run Banana command some more. Tests don't update.

Expected behaviour: tests get added/removed

I am opening a PR