Merge branch '238601-clarify-when-CI_COMMIT_BRANCH-is-present' into 'master'

Clarify when CI_COMMIT_BRANCH is present

See merge request gitlab-org/gitlab!47593

doc/ci/variables/predefined_variables.md

@@ -40,7 +40,7 @@ Kubernetes-specific environment variables are detailed in the
 | `CI_COMMIT_REF_SLUG`                          | 9.0    | all    | `$CI_COMMIT_REF_NAME` lowercased, shortened to 63 bytes, and with everything except `0-9` and `a-z` replaced with `-`. No leading / trailing `-`. Use in URLs, host names and domain names.                                                                                                                                                                |
 | `CI_COMMIT_SHA`                               | 9.0    | all    | The commit revision for which project is built                                                                                                                                                                                                                                                                                                             |
 | `CI_COMMIT_SHORT_SHA`                         | 11.7   | all    | The first eight characters of `CI_COMMIT_SHA`                                                                                                                                                                                                                                                                                                              |
-| `CI_COMMIT_BRANCH`                            | 12.6   | 0.5    | The commit branch name. Present only when building branches.                                                                                                                                                                                                                                                                                                      |
+| `CI_COMMIT_BRANCH`                            | 12.6   | 0.5    | The commit branch name. Present in branch pipelines, including pipelines for the default branch. Not present in merge request pipelines.                                                                                                                                                                                                                                                                                                      |
 | `CI_COMMIT_TAG`                               | 9.0    | 0.5    | The commit tag name. Present only when building tags.                                                                                                                                                                                                                                                                                                      |
 | `CI_COMMIT_TITLE`                             | 10.8   | all    | The title of the commit - the full first line of the message                                                                                                                                                                                                                                                                                               |
 | `CI_COMMIT_TIMESTAMP`                         | 13.4   | all    | The timestamp of the commit in the ISO 8601 format.                                                                                                                                                                                                                                                                                               |