Fix other API change: body renamed to filename

libraries/matrix/test/src/main/kotlin/io/element/android/libraries/matrix/test/media/FakeMatrixMediaLoader.kt

@@ -35,7 +35,7 @@ class FakeMatrixMediaLoader : MatrixMediaLoader {
     override suspend fun downloadMediaFile(
         source: MediaSource,
         mimeType: String?,
-        body: String?,
+        filename: String?,
         useCache: Boolean,
     ): Result<MediaFile> = simulateLongTask {
         if (shouldFail) {