Merge branch 'doc/variables-in-rules' into 'master'

mention `rules` in documentation where variables can be used

See merge request gitlab-org/gitlab!57806

doc/ci/variables/where_variables_can_be_used.md

@@ -35,7 +35,7 @@ There are two places defined variables can be used. On the:
 | `cache:key`                                | yes              | Runner                 | The variable expansion is made by GitLab Runner's [internal variable expansion mechanism](#gitlab-runner-internal-variable-expansion-mechanism)                                                                                                                                                                                                                                                                                   |
 | `artifacts:name`                           | yes              | Runner                 | The variable expansion is made by GitLab Runner's shell environment                                                                                                                                                                                                                                                                                                                                                               |
 | `script`, `before_script`, `after_script`  | yes              | Script execution shell | The variable expansion is made by the [execution shell environment](#execution-shell-environment)                                                                                                                                                                                                                                                                                                                                 |
-| `only:variables:[]`, `except:variables:[]` | no               | n/a                    | The variable must be in the form of `$variable`. Not supported are the following:<br/><br/>- Variables that are based on the environment's name (`CI_ENVIRONMENT_NAME`, `CI_ENVIRONMENT_SLUG`).<br/>- Any other variables related to environment (currently only `CI_ENVIRONMENT_URL`).<br/>- [Persisted variables](#persisted-variables).                                                                                            |
+| `only:variables:[]`, `except:variables:[]`, `rules:if` | no               | n/a                    | The variable must be in the form of `$variable`. Not supported are the following:<br/><br/>- Variables that are based on the environment's name (`CI_ENVIRONMENT_NAME`, `CI_ENVIRONMENT_SLUG`).<br/>- Any other variables related to environment (currently only `CI_ENVIRONMENT_URL`).<br/>- [Persisted variables](#persisted-variables).                                                                                            |
 
 ### `config.toml` file