Use US English Spelling for BehaviorSubject.

This represents a class in the RxJava library. Not saying US English is
better, but it is.

https://github.com/ReactiveX/RxJava/blob/2.x/src/main/java/io/reactivex/subjects/BehaviorSubject.java

Author: Nelson Osacky

binary-compatibility-validator/reference-public-api/kotlinx-coroutines-core.txt

@@ -826,7 +826,7 @@ public abstract interface class kotlinx/coroutines/flow/FlowCollector {
 
 public final class kotlinx/coroutines/flow/FlowKt {
 	public static final field DEFAULT_CONCURRENCY_PROPERTY_NAME Ljava/lang/String;
-	public static final fun BehaviourSubject ()Ljava/lang/Object;
+	public static final fun BehaviorSubject ()Ljava/lang/Object;
 	public static final fun PublishSubject ()Ljava/lang/Object;
 	public static final fun ReplaySubject ()Ljava/lang/Object;
 	public static final fun asFlow (Ljava/lang/Iterable;)Lkotlinx/coroutines/flow/Flow;

kotlinx-coroutines-core/common/src/flow/Migration.kt

@@ -104,7 +104,7 @@ public fun <T> Flow<T>.subscribeOn(context: CoroutineContext): Flow<T> = noImpl(
  * @suppress
  */
 @Deprecated(message = "Use BroadcastChannel.asFlow()", level = DeprecationLevel.ERROR)
-public fun BehaviourSubject(): Any = noImpl()
+public fun BehaviorSubject(): Any = noImpl()
 
 /**
  * `ReplaySubject` is not supported. The closest analogue is buffered [BroadcastChannel][kotlinx.coroutines.channels.BroadcastChannel].