🐛 Add missing started_riding trigger

java/data/advancement/trigger.mcdoc

@@ -130,6 +130,7 @@ dispatch minecraft:trigger[effects_changed] to Conditions<struct EffectsChanged
 	effects?: struct {
 		[#[id="mob_effect"] string]: MobEffectPredicate,
 	},
+	#[since="1.17"]
 	source?: CompositeEntity,
 }>
 
@@ -374,6 +375,9 @@ dispatch minecraft:trigger[slide_down_block] to Conditions<struct SlideDownBlock
 	block?: #[id="block"] string,
 }>
 
+#[since="1.17"]
+dispatch minecraft:trigger[started_riding] to Conditions<TriggerBase>
+
 /// Activated when the last required block is placed for summoning
 /// iron golems (pumpkin and iron blocks), snow golems (pumpkin and snow blocks), the ender dragon (end crystals),
 /// or the wither (wither skulls and soul sand/soul soil).