Fix InboundDecoderTests.testDecodePreHeaderSizeVariableInt() (elastic#132215)

This test needed to be updated when elastic#123390 was backported
to 8.19 in elastic#123554 since the test didn't exist on main when
elastic#123390 was merged.

Author: JeremyDahlgren

server/src/test/java/org/elasticsearch/transport/InboundDecoderTests.java

@@ -163,7 +163,6 @@ public void testDecodePreHeaderSizeVariableInt() throws IOException {
                 assertEquals(3, fragments.size());
                 final Object body = fragments.get(1);
                 assertThat(body, instanceOf(ReleasableBytesReference.class));
-                ((ReleasableBytesReference) body).close();
             }
             assertEquals(InboundDecoder.END_CONTENT, fragments.get(fragments.size() - 1));
             assertEquals(totalBytes.length() - bytesConsumed, bytesConsumed2);