chore: migrate three packages to MSW v2

Migrates test files in config-loader, events-node and kubernetes-react
packages from MSW 1.x to MSW 2.x API to fix compatibility issues with
Jest 30 and JSDOM v26.

Changes:
- Updated msw dependency from ^1.0.0 to ^2.0.0
- Changed imports from `rest` to `http` and `HttpResponse`
- Converted handler syntax from `res(ctx.*)` to `HttpResponse.*`
- Changed `toStrictEqual` to `toEqual` for response assertions

Affected packages:
- @backstage/config-loader
- @backstage/plugin-events-node
- @backstage/plugin-kubernetes-react

Signed-off-by: Johan Persson <johanopersson@gmail.com>

plugins/events-node/package.json

@@ -65,7 +65,7 @@
   "devDependencies": {
     "@backstage/backend-test-utils": "workspace:^",
     "@backstage/cli": "workspace:^",
-    "msw": "^1.0.0"
+    "msw": "^2.0.0"
   },
   "configSchema": "config.d.ts"
 }