Fix a suppressed warning

This also fixes the build with the in-development 1.8.0 Kotlin
compiler.

Before, when constructing `Maybe<A & Any>`, we had `T = A?`.
This way, `MaybeEmitter<T & Any>` meant `MaybeEmitter<A? & Any>`.
However, with the new version, type inference must have changed,
so it came to be that `T = A`, breaking the code.

Author: dkhalanskyjb

reactive/kotlinx-coroutines-rx3/src/RxMaybe.kt

@@ -37,13 +37,12 @@ private fun <T> rxMaybeInternal(
     coroutine.start(CoroutineStart.DEFAULT, coroutine, block)
 }
 
-private class RxMaybeCoroutine<T>(
+private class RxMaybeCoroutine<T: Any>(
     parentContext: CoroutineContext,
-    private val subscriber: MaybeEmitter<T & Any>
-) : AbstractCoroutine<T>(parentContext, false, true) {
-    override fun onCompleted(value: T) {
+    private val subscriber: MaybeEmitter<T>
+) : AbstractCoroutine<T?>(parentContext, false, true) {
+    override fun onCompleted(value: T?) {
         try {
-            @Suppress("NULLABILITY_MISMATCH_BASED_ON_JAVA_ANNOTATIONS") // KT-54201
             if (value == null) subscriber.onComplete() else subscriber.onSuccess(value)
         } catch (e: Throwable) {
             handleUndeliverableException(e, context)