Add additional limitation to `needs` keyword

doc/ci/pipelines/multi_project_pipelines.md

@@ -88,7 +88,7 @@ The keywords available for use in trigger jobs are:
 - [`only` and `except`](../yaml/index.md#only--except)
 - [`when`](../yaml/index.md#when) (only with a value of `on_success`, `on_failure`, or `always`)
 - [`extends`](../yaml/index.md#extends)
-- [`needs`](../yaml/index.md#needs)
+- [`needs`](../yaml/index.md#needs), but not [cross project artifact downloads with `needs`](../yaml/index.md#cross-project-artifact-downloads-with-needs)
 
 #### Specify a downstream pipeline branch
 

doc/ci/yaml/index.md

@@ -1703,6 +1703,8 @@ same group or namespace, you can omit them from the `project:` keyword. For exam
 
 The user running the pipeline must have at least `reporter` access to the group or project, or the group/project must have public visibility.
 
+You cannot use cross project artifact downloads in the same job as [`trigger`](#trigger).
+
 ##### Artifact downloads between pipelines in the same project
 
 Use `needs` to download artifacts from different pipelines in the current project.