Issue #3426292 Deprecate and rename two variables

Closes #3426292

docs/jobs/composer.md

@@ -10,7 +10,7 @@ When testing against future releases, dependencies may not be compatible with th
 
 ### Lenient support
 
-The variable `LENIENT_ALLOW_LIST` can specify a comma-separated list of modules that composer dependencies on the core version will be ignored for. This is achieved using the [mglaman/composer-drupal-lenient](https://github.com/mglaman/composer-drupal-lenient) composer extension.
+The variable `_LENIENT_ALLOW_LIST` can specify a comma-separated list of modules that composer dependencies on the core version will be ignored for. This is achieved using the [mglaman/composer-drupal-lenient](https://github.com/mglaman/composer-drupal-lenient) composer extension.
 
 An example of this can be:
 ```
@@ -21,11 +21,11 @@ variables:
 
 composer (next minor):
   variables:
-    LENIENT_ALLOW_LIST: token
+    _LENIENT_ALLOW_LIST: token
 
 composer (next major):
   variables:
-    LENIENT_ALLOW_LIST: entity_reference_revisions,inline_entity_form,paragraphs,token
+    _LENIENT_ALLOW_LIST: entity_reference_revisions,inline_entity_form,paragraphs,token
 ```
 
 In this example, the lenient plugin will NOT be used in the regular composer task. But it will be used for the next minor and next major with different lists of projects that are allowed, even if those projects are not compatible with the new release.
@@ -35,12 +35,12 @@ In this example, the lenient plugin will NOT be used in the regular composer tas
 
 Sometimes, you may need to install a patch for a dependent module to allow tests to pass.
 
-To this, add a JSON file containing patches, and specify it in the `COMPOSER_PATCHES_FILE` variable. For example:
+To this, add a JSON file containing patches, and specify it in the `_COMPOSER_PATCHES_FILE` variable. For example:
 ```
 composer (next major):
   variables:
-    LENIENT_ALLOW_LIST: token
-    COMPOSER_PATCHES_FILE: .gitlab-ci/nextmajor_patches.json
+    _LENIENT_ALLOW_LIST: token
+    _COMPOSER_PATCHES_FILE: .gitlab-ci/nextmajor_patches.json
 ```
 
 We recommend placing the patches within the `.gitlab-ci` folder inside your module.