Add C API dependencies installation to workflow

.github/workflows/capi.yml

@@ -15,6 +15,12 @@ jobs:
         uses: actions/setup-python@v4
         with:
           python-version: "3.10"
+      - name: Install dependencies
+        run: |
+          # build dependencies
+          pip install cffi
+          # runtime dependencies
+          pip install .
       - name: Build & install library
         working-directory: ./capi
         run: |