Merge branch 'docs/zm-rspec-meta-mixedenv' into 'master'

Update rspec metadata list

See merge request gitlab-org/gitlab!70103

doc/development/testing_guide/end_to_end/rspec_metadata_tests.md

@@ -26,6 +26,7 @@ This is a partial list of the [RSpec metadata](https://relishapp.com/rspec/rspec
 | `:ldap_no_tls`    | The test requires a GitLab instance to be configured to use an external LDAP server with TLS not enabled. |
 | `:ldap_tls`       | The test requires a GitLab instance to be configured to use an external LDAP server with TLS enabled. |
 | `:mattermost`     | The test requires a GitLab Mattermost service on the GitLab instance. |
+| `:mixed_env`      | The test should only be executed in environments that have a paired canary version available through traffic routing based on the existence of the `gitlab_canary=true` cookie. Tests in this category are switching the cookie mid-test to validate mixed deployment environments. |
 | `:object_storage` | The test requires a GitLab instance to be configured to use multiple [object storage types](../../../administration/object_storage.md). Uses MinIO as the object storage server. |
 | `:only`           | The test is only to be run in specific execution contexts. See [test execution context selection](execution_context_selection.md) for more information. |
 | `:orchestrated`   | The GitLab instance under test may be [configured by `gitlab-qa`](https://gitlab.com/gitlab-org/gitlab-qa/-/blob/master/docs/what_tests_can_be_run.md#orchestrated-tests) to be different to the default GitLab configuration, or `gitlab-qa` may launch additional services in separate Docker containers, or both. Tests tagged with `:orchestrated` are excluded when testing environments where we can't dynamically modify the GitLab configuration (for example, Staging). |