Fixed link to available variables

lib/gitlab/ci/templates/Security/Secret-Detection.gitlab-ci.yml

 # Read more about this feature here: https://docs.gitlab.com/ee/user/application_security/secret_detection
 #
 # Configure the scanning tool through the environment variables.
-# List of the variables: https://gitlab.com/gitlab-org/security-products/secret_detection#available-variables
+# List of the variables: https://docs.gitlab.com/ee/user/application_security/secret_detection/#available-variables
 # How to set: https://docs.gitlab.com/ee/ci/yaml/#variables
 
 variables: