ci: remove unused cache step

.github/workflows/ci.yml

@@ -134,14 +134,6 @@ jobs:
           git config --global --add safe.directory $GITHUB_WORKSPACE
           git fetch --tags --force
 
-      - name: Cache vcpkg dir
-        uses: actions/cache@v4
-        with:
-          path: |
-            ${{github.workspace}}/build/vcpkg
-
-          key: vcpkg-${{ runner.os }}-1
-
       # This effectively runs `vcvarsall.bat`, etc. It's not actually installing
       # VC++ as that's already pre-installed on the Windows runner.
       - name: Setup VC++ environment