ci: install observer.py dependencies

Signed-off-by: Pau Ruiz Safont <pau.ruizsafont@cloud.com>

.github/workflows/main.yml

@@ -51,7 +51,7 @@ jobs:
 
       - name: Install dependencies only needed for python 3
         if: ${{ matrix.python-version != '2.7' }}
-        run: pip install pandas pytype toml wrapt
+        run: pip install opentelemetry-api opentelemetry-exporter-zipkin-json opentelemetry-sdk pandas pytype toml wrapt
 
       - name: Install common dependencies for Python ${{matrix.python-version}}
         run: pip install future mock pytest-coverage pytest-mock