Update GitLab CI/CD for tests

• remove pipenv before running tests
• install opensearch extra

.gitlab-ci.yml

@@ -8,7 +8,8 @@ run-tests:
   stage: testing
   script:
     - pip install --upgrade pip pipenv
-    - pipenv run pip install -e '.[tests]'
+    - pipenv --rm
+    - pipenv run pip install -e '.[tests,opensearch2]'
     - pipenv run ./run-tests.sh
   coverage: /TOTAL.*? (100(?:\.0+)?\%|[1-9]?\d(?:\.\d+)?\%)$/