Adding a note the variable is read-only once the pipeline has started.

doc/ci/variables/predefined_variables.md

@@ -38,7 +38,7 @@ There are also [Kubernetes-specific deployment variables](../../user/project/clu
 | `CI_COMMIT_TITLE`                        | 10.8   | all    | The title of the commit. The full first line of the message. |
 | `CI_CONCURRENT_ID`                       | all    | 11.10  | The unique ID of build execution in a single executor. |
 | `CI_CONCURRENT_PROJECT_ID`               | all    | 11.10  | The unique ID of build execution in a single executor and project. |
-| `CI_CONFIG_PATH`                         | 9.4    | 0.5    | The path to the CI/CD configuration file. Defaults to `.gitlab-ci.yml`. |
+| `CI_CONFIG_PATH`                         | 9.4    | 0.5    | The path to the CI/CD configuration file. Defaults to `.gitlab-ci.yml`. Read-only inside a running pipeline. |
 | `CI_DEBUG_TRACE`                         | all    | 1.7    | `true` if [debug logging (tracing)](index.md#debug-logging) is enabled. |
 | `CI_DEFAULT_BRANCH`                      | 12.4   | all    | The name of the project's default branch. |
 | `CI_DEPENDENCY_PROXY_GROUP_IMAGE_PREFIX` | 13.7   | all    | The image prefix for pulling images through the Dependency Proxy. |