ci(docs-infra): ensure `aio_monitoring` failure notifications do not depend on earlier steps (#28555)

Previously, in order for the `aio_monitoring` failure notifications to
work, the steps up to `define_env_vars` should have succeeded. This
meant that any failures in earlier steps would not send notifications.

This commit fixes it by making the notification step independent of the
`define_env_vars` step.

PR Close #28555

.circleci/config.yml

@@ -458,7 +458,9 @@ jobs:
           command: ./aio/scripts/test-production.sh $CI_AIO_MIN_PWA_SCORE
       - run:
           name: Notify caretaker about failure
-          command: 'curl --request POST --header "Content-Type: application/json" --data "{\"text\":\":x: \`$CIRCLE_JOB\` job failed on build $CIRCLE_BUILD_NUM: $CIRCLE_BUILD_URL :scream:\"}" $CI_SECRET_SLACK_CARETAKER_WEBHOOK_URL'
+          # `$SLACK_CARETAKER_WEBHOOK_URL` is a secret env var defined in CircleCI project settings.
+          # The URL comes from https://angular-team.slack.com/apps/A0F7VRE7N-circleci.
+          command: 'curl --request POST --header "Content-Type: application/json" --data "{\"text\":\":x: \`$CIRCLE_JOB\` job failed on build $CIRCLE_BUILD_NUM: $CIRCLE_BUILD_URL :scream:\"}" $SLACK_CARETAKER_WEBHOOK_URL'
           when: on_fail
 
   legacy-unit-tests-local:

.circleci/env.sh

@@ -39,8 +39,6 @@ setPublicVar CI_YARN_VERSION "1.13.0";
 ####################################################################################################
 setSecretVar CI_SECRET_AIO_DEPLOY_FIREBASE_TOKEN "$AIO_DEPLOY_TOKEN";
 setSecretVar CI_SECRET_PAYLOAD_FIREBASE_TOKEN "$ANGULAR_PAYLOAD_TOKEN";
-# Defined in https://angular-team.slack.com/apps/A0F7VRE7N-circleci.
-setSecretVar CI_SECRET_SLACK_CARETAKER_WEBHOOK_URL "$SLACK_CARETAKER_WEBHOOK_URL";
 
 
 ####################################################################################################