test(deps): bump ws to ^8.21.0 in brainstorm-server tests

Clears two dependabot alerts on the test harness's ws dependency:
GHSA-96hv-2xvq-fx4p (high, memory-exhaustion DoS, fixed 8.21.0) and
GHSA-58qx-3vcg-4xpx (medium, uninitialized memory disclosure, fixed
8.20.1). Test-only — the shipped brainstorm server hand-rolls its
WebSocket framing and does not depend on ws. Suite passes (57/57).

tests/brainstorm-server/package-lock.json

@@ -8,13 +8,13 @@
       "name": "brainstorm-server-tests",
       "version": "1.0.0",
       "dependencies": {
-        "ws": "^8.19.0"
+        "ws": "^8.21.0"
       }
     },
     "node_modules/ws": {
-      "version": "8.19.0",
-      "resolved": "https://registry.npmjs.org/ws/-/ws-8.19.0.tgz",
-      "integrity": "sha512-blAT2mjOEIi0ZzruJfIhb3nps74PRWTCz1IjglWEEpQl5XS/UNama6u2/rjFkDDouqr4L67ry+1aGIALViWjDg==",
+      "version": "8.21.0",
+      "resolved": "https://registry.npmjs.org/ws/-/ws-8.21.0.tgz",
+      "integrity": "sha512-Vsp28b7DRcimFQvrqu2Wek3z1iYxDCWqHYB8Qsnk/S4RfaCQzPGPyBNuVjJV3cd6UiKtUtp6sNM77gWvzcCH+g==",
       "license": "MIT",
       "engines": {
         "node": ">=10.0.0"

tests/brainstorm-server/package.json

@@ -5,6 +5,6 @@
     "test": "node ws-protocol.test.js && node helper.test.js && node browser-launcher.test.js && node auth.test.js && node branding.test.js && node server.test.js && node lifecycle.test.js && bash start-server.test.sh && bash stop-server.test.sh"
   },
   "dependencies": {
-    "ws": "^8.19.0"
+    "ws": "^8.21.0"
   }
 }