add gtk install step to windows ci

.github/workflows/ci.yml

@@ -90,6 +90,16 @@ jobs:
           cache: "pip"
           cache-dependency-path: "requirements*.txt"
 
+      - name: Install GTK
+        run: |
+          $WebClient = New-Object System.Net.WebClient
+          $WebClient.DownloadFile("https://github.com/${{ github.repository_owner }}/gvsbuild-release/releases/download/latest/gvsbuild-py${{ matrix.python }}-vs16-${{ matrix.arch }}.zip","C:\GTK.zip")
+          7z x C:\GTK.zip -oc:\GTK
+          echo "C:\GTK\release\lib" | Out-File -FilePath $env:GITHUB_PATH -Append
+          echo "C:\GTK\release\bin" | Out-File -FilePath $env:GITHUB_PATH -Append
+          echo "C:\GTK\release" | Out-File -FilePath $env:GITHUB_PATH -Append
+          python -m pip install --no-index --find-links="C:\GTK\release\python" pycairo PyGObject
+
       - name: Install dependencies
         run: |
           pip install --upgrade pip wheel setuptools