ci: install libyaml when appropriate

.github/workflows/build.yml

@@ -30,6 +30,9 @@ jobs:
         uses: actions/setup-python@v2
         with:
           python-version: 2.7
+      - if: matrix.os == 'ubuntu-latest'
+        run: |
+          apt-get install -y libyaml-dev
       - name: Install PyInstaller
         # pyinstaller 4 doesn't support Python 2.7
         run: pip install 'pyinstaller==3.*'

.github/workflows/tests.yml

@@ -61,6 +61,8 @@ jobs:
       uses: actions/setup-python@v2
       with:
         python-version: ${{ matrix.python }}
+    - name: Install pyyaml
+      run: apt-get install -y libyaml-dev
     - name: Install capa
       run: pip install -e .[dev]
     - name: Run tests