CI: remove manual PowerShell install from test-proxy job (e2e-tests.yml) (#703)

* fix basic validation with npm command

* Revert "fix basic validation with npm command"

This reverts commit 27a0803a2a.

* replace ubuntu:22.04 with devcontainer image to remove unsafe powershell install

.github/workflows/e2e-tests.yml

@@ -495,7 +495,7 @@ jobs:
   test-proxy:
     runs-on: ubuntu-22.04
     container:
-      image: ubuntu:22.04
+      image: mcr.microsoft.com/devcontainers/dotnet:10.0
       options: --dns 127.0.0.1
     services:
       squid-proxy:
@@ -508,15 +508,6 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v6
-      - name: Install Powershell
-        run: |
-          apt-get update
-          apt-get install -y wget apt-transport-https software-properties-common
-          wget -q "https://packages.microsoft.com/config/ubuntu/$(lsb_release -rs)/packages-microsoft-prod.deb"
-          dpkg -i packages-microsoft-prod.deb
-          rm packages-microsoft-prod.deb
-          apt-get update
-          apt-get install -y powershell
       - name: Clear toolcache
         shell: pwsh
         run: __tests__/clear-toolcache.ps1 ${{ runner.os }}