Report pipeline failures for stable branches in FOSS project

This is in response to gitlab-org/gitlab#412717 (comment 1748043789) to make sure that we're notified for stable branches failures for the FOSS project.

Looks like this can be easily done like in Triage::PipelineFailure::Config::MasterBranch as:

diff --git a/triage/triage/pipeline_failure/config/stable_branch.rb b/triage/triage/pipeline_failure/config/stable_branch.rb
index be22e09f..c985d8eb 100644
--- a/triage/triage/pipeline_failure/config/stable_branch.rb
+++ b/triage/triage/pipeline_failure/config/stable_branch.rb
@@ -45,10 +45,11 @@ module Triage
         MARKDOWN
 
         SLACK_CHANNEL = 'releases'
+        APPLICABLE_PROJECT_PATHS = ['gitlab-org/gitlab', 'gitlab-org/gitlab-foss'].freeze
 
         def self.match?(event)
           event.on_instance?(:com) &&
-            event.project_path_with_namespace == 'gitlab-org/gitlab' &&
+            APPLICABLE_PROJECT_PATHS.include?(event.project_path_with_namespace) &&
             event.ref.match?(/^[\d-]+-stable(-ee)?$/) &&
             event.source_job_id.nil? # exclude triggered pipeline
         end