CI: Fix setting up test database

Rails will complain that we have setup the sandbox database
in development environment, so we need to reset the db env
to test.

.circleci/config.yml

@@ -47,10 +47,12 @@ jobs:
           name: "Runs tests on Solidus <<parameters.solidus_branch>>"
           command: |
             cd sandbox
+            bin/rails db:environment:set RAILS_ENV=test
             bundle add rspec_junit_formatter --group test
             <<#parameters.coverage>>export COVERAGE=true<</parameters.coverage>>
             bundle exec rspec --format progress --format RspecJunitFormatter --out ../test-results/results.xml
           environment:
+            RAILS_ENV: test
             RAILS_VERSION: <<parameters.rails_version>>
             SOLIDUS_BRANCH: <<parameters.solidus_branch>>
           when: always