fix build

Author: cekk

.github/workflows/test.yml

@@ -24,6 +24,7 @@ jobs:
       - name: Install dependencies
         run: |
           pip install -r requirements.txt -c constraints_plone${{ matrix.plone }}.txt
+          pip install zc.buildout=3.3
           sudo apt-get install libtiff5-dev libjpeg8-dev libopenjp2-7-dev zlib1g-dev \
             libfreetype6-dev liblcms2-dev libwebp-dev tcl8.6-dev tk8.6-dev python3-tk \
             libharfbuzz-dev libfribidi-dev libxcb1-dev