Set DISPLAY in github actions

Author: paulacamargo25

.github/workflows/pr-check.yml

@@ -93,9 +93,12 @@ jobs:
       - name: Start xvfb on Linux
         run: |
           /usr/bin/Xvfb :99 -screen 0 1024x768x24 > /dev/null 2>&1 &
+          echo "DISPLAY=:99" >> $GITHUB_ENV
           echo ">>> Started xvfb"
         if: ${{ runner.os }} == 'Linux'
 
       - name: Run tests
         run: python -m nox --session tests
         shell: bash
+        env:
+          DISPLAY: ${{ env.DISPLAY }}