ci: Install pkgconfig for OpenCV 4

Author: auscompgeek

.github/workflows/ci.yml

@@ -24,14 +24,19 @@ jobs:
       - uses: actions/checkout@v1
         with:
           submodules: true
+
       - name: Add OpenCV 3.4 PPA
         if: matrix.os == 'ubuntu-18.04'
         run: sudo add-apt-repository -y ppa:~timsc/opencv-3.4
+
       - name: Install dependencies
         run: |
           sudo apt-get install --no-install-recommends -y \
             libopencv-dev python3-opencv
-      - run: python3 -m pip install setuptools wheel
+
+      - name: Install Python setup requirements
+        run: python3 -m pip install setuptools wheel pkgconfig
+
       - run: python3 setup.py sdist
       - run: python3 -m pip install dist/*.tar.gz
       - run: python3 -m cscore --help