Disable selective execution when target branch is stable branch

qa/qa/tools/ci/qa_changes.rb

@@ -45,7 +45,7 @@ def qa_tests
         #
         # @return [String]
         def fetch_list_of_specs_or_directories
-          if QA::Runtime::Env.selective_execution_improved_enabled? && non_qa_changes?
+          if QA::Runtime::Env.selective_execution_improved_enabled? && non_qa_changes? && !targeting_stable_branch?
             tests = selective_tests_from_code_paths_mapping
             logger.info("Selected tests from mapping: '#{tests}'")
             tests.nil? || tests.empty? ? nil : tests.join(" ")
@@ -67,6 +67,10 @@ def framework_changes?
             .any?
         end
+        def targeting_stable_branch?
+          /^[\d-]+-stable(-ee|-jh)?$/.match?(ENV['CI_MERGE_REQUEST_TARGET_BRANCH_NAME'])
+        end
+
         def quarantine_changes?
           return false if mr_diff.empty?
           return false if mr_diff.any? { |change| change[:new_file] || change[:deleted_file] }