Use variableNode for trace_propagation_targets

Author: cleptric

src/DependencyInjection/Configuration.php

@@ -91,10 +91,7 @@ public function getConfigTreeBuilder(): TreeBuilder
                             ->info('The sampling factor to apply to profiles. A value of 0 will deny sending any profiles, and a value of 1 will send all profiles. Profiles are sampled in relation to traces_sample_rate')
                         ->end()
                         ->scalarNode('traces_sampler')->end()
-                        ->arrayNode('trace_propagation_targets')
-                            ->scalarPrototype()->end()
-                            ->beforeNormalization()->castToArray()->end()
-                        ->end()
+                        ->variableNode('trace_propagation_targets')->end()
                         ->booleanNode('attach_stacktrace')->end()
                         ->integerNode('context_lines')->min(0)->end()
                         ->booleanNode('enable_compression')->end()