test: run kaggle-environments tests in jenkins pipeline (#1535)

BUG=b/477947477

A bit of a quick and dirty solution to the ask. It's brittle against
things like simple file moves in the `kaggle-environments` repo, but
wasn't too sure how much we really wanted to couple these two repos.
Open to alternative implementations.

Author: KeijiBranshi

Jenkinsfile

@@ -169,6 +169,21 @@ pipeline {
             }
           }
         }
+        stage('Test kaggle-environments') {
+          options {
+            timeout(time: 15, unit: 'MINUTES')
+          }
+          steps {
+            sh '''#!/bin/bash
+              set -exo pipefail
+              docker run --rm \
+                -e PYTHONUNBUFFERED=1 \
+                --pull always \
+                gcr.io/kaggle-images/python:${PRETEST_TAG} \
+                bash -c "git clone https://github.com/Kaggle/kaggle-environments.git /tmp/kaggle-environments && cd /tmp/kaggle-environments && python -m pytest tests/ kaggle_environments/ --tb=short"
+            '''
+          }
+        }
       }
     }