[gitlab-ci] Change PREFIX to use conda environement

.gitlab-ci.yml

@@ -2,10 +2,10 @@ stages:
   - build
 
 variables:
-  PREFIX: /opt/beat.env.web/usr
   TEST_PREFIX_PATH_FILE: 'test_prefix_$CI_JOB_ID.txt'
   CONDA_ENV_NAME: beat_test_env
   CONDA_PREFIX: /local/opt/conda
+  PREFIX: $CONDA_PREFIX/envs/$CONDA_ENV_NAME
 
 build:
   stage: build