GitHub Actions: install cairo on Windows

Author: brechtm

.github/workflows/tests.yml

@@ -276,6 +276,8 @@ jobs:
       if: startsWith(runner.os, 'Windows')
       run: |
         choco install mupdf --version=1.26.0
+        choco install gtk-runtime   # includes cairo
+        RefreshEnv.cmd
 
     - name: Run Nox
       run: ${{ env.nox_cmd }} ${{ env.NOXENV }} -- -s