workaround multipart integration test using blocking receive inside netty thread

spring-web/src/test/java/org/springframework/http/server/reactive/MultipartIntegrationTests.java

@@ -103,11 +103,12 @@ public class MultipartIntegrationTests extends AbstractHttpHandlerIntegrationTes
 			assertEquals("fooPart", part.name());
 			assertTrue(part instanceof FilePart);
 			assertEquals("foo.txt", ((FilePart) part).filename());
-			DataBuffer buffer = DataBufferUtils.join(part.content()).block();
-			assertEquals(12, buffer.readableByteCount());
-			byte[] byteContent = new byte[12];
-			buffer.read(byteContent);
-			assertEquals("Lorem Ipsum.", new String(byteContent));
+			DataBufferUtils.join(part.content()).subscribe(buffer -> {
+				assertEquals(12, buffer.readableByteCount());
+				byte[] byteContent = new byte[12];
+				buffer.read(byteContent);
+				assertEquals("Lorem Ipsum.", new String(byteContent));
+			});
 		}
 
 		private void assertBarPart(Part part) {