Make the test more lenient with timing.

Author: garydgregory

src/test/java/org/apache/commons/io/input/ReadAheadInputStreamTest.java

@@ -96,7 +96,9 @@ void testClosePlusExecutorService() throws IOException {
                 try (ReadAheadInputStream rais = ReadAheadInputStream.builder().setInputStream(inputStream).setExecutorService(externalExecutor).get()) {
                     assertEquals('1', rais.read());
                 }
+                Thread.yield();
                 // The underlying FileInputStream should be closed since ReadAheadInputStream is a FilterInputStream.
+                assertThrows(IOException.class, inputStream::available);
                 assertThrows(IOException.class, inputStream::read);
                 // The caller remains responsible for shutting down the executor.
             } finally {