Downgrade ws to 8.20.0 to match dnceng mirror availability

The dnceng dotnet-public-npm mirror has not yet mirrored ws@8.20.1 or
ws@8.21.0, causing 401 Unauthorized errors when CI restores extension/yarn.lock
(`yarn install --frozen-lockfile` failed in Tests / Run VS Code extension tests`(Windows)`). The same broken URLs would later break `npm ci` in the Angular
and React playground fixtures.

ws@8.20.0 is already in the mirror and still resolves the underlying
security advisory (GHSA-3h5v-q93c-6h6q, fixed in 8.17.1).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: IEvangelist

extension/package.json

@@ -941,7 +941,7 @@
     "tree-sitter-c-sharp": "0.23.5",
     "vscode-jsonrpc": "8.2.1",
     "web-tree-sitter": "0.26.9",
-    "ws": "8.20.1"
+    "ws": "8.20.0"
   },
   "resolutions": {
     "braces": "3.0.3",

extension/yarn.lock

@@ -6007,10 +6007,10 @@ wrappy@1:
   resolved "https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-public-npm/npm/registry/wrappy/-/wrappy-1.0.2.tgz"
   integrity sha1-tSQ9jz7BqjXxNkYFvA0QNuMKtp8=
 
-ws@8.20.1:
-  version "8.20.1"
-  resolved "https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-public-npm/npm/registry/ws/-/ws-8.20.1.tgz#91a9ae2b312ccf98e0a85ec499b48cef45ab0ddb"
-  integrity sha1-kamuKzEsz5jgqF7EmbSM70WrDds=
+ws@8.20.0:
+  version "8.20.0"
+  resolved "https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-public-npm/npm/registry/ws/-/ws-8.20.0.tgz"
+  integrity sha1-TNlTI1jrpgvIY6rRYj37BFpNSvg=
 
 wsl-utils@^0.1.0:
   version "0.1.0"