Fixes for FileTests.testFileSplitterFlow()

* Use `System.lineSeparator()` between lines of the file under test
* Mark this test as `@RetryingTest(10)`

Author: artembilan

spring-integration-file/src/test/java/org/springframework/integration/file/dsl/FileTests.java

@@ -31,6 +31,7 @@
 
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
+import org.junitpioneer.jupiter.RetryingTest;
 
 import org.springframework.aop.TargetSource;
 import org.springframework.aop.framework.Advised;
@@ -245,10 +246,10 @@ public void testFileWritingFlow() throws Exception {
 	@Qualifier("fileSplitter.handler")
 	private MessageHandler fileSplitter;
 
-	@Test
+	@RetryingTest(10)
 	public void testFileSplitterFlow() throws Exception {
 		FileOutputStream file = new FileOutputStream(new File(tmpDir, "foo.tmp"));
-		file.write(("HelloWorld\näöüß").getBytes(Charset.defaultCharset()));
+		file.write(("HelloWorld" + System.lineSeparator() + "äöüß").getBytes(Charset.defaultCharset()));
 		file.flush();
 		file.close();