copying the list of new session listeners to avoid concurrent modification

- copying the list avoids the need to synchronise the add/removing/iterations

changelog.d/5746.bugfix

@@ -0,0 +1 @@
+Fixes crash when navigating the app whilst processing new room keys

matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/crypto/RoomDecryptorProvider.kt

@@ -74,7 +74,7 @@ internal class RoomDecryptorProvider @Inject constructor(
                     this.newSessionListener = object : NewSessionListener {
                         override fun onNewSession(roomId: String?, senderKey: String, sessionId: String) {
                             // PR reviewer: the parameter has been renamed so is now in conflict with the parameter of getOrCreateRoomDecryptor
-                            newSessionListeners.forEach {
+                            newSessionListeners.toList().forEach {
                                 try {
                                     it.onNewSession(roomId, senderKey, sessionId)
                                 } catch (e: Throwable) {