appender: temporarily ignore flaky test (#752)

See #751.

This is a temporary stop-gap solution until we get a better
understanding of what's going on here. I don't want it to block
unrelated changes to other crates in the meantime.

Signed-off-by: Eliza Weisman <eliza@buoyant.io>

tracing-appender/src/non_blocking.rs

@@ -341,6 +341,7 @@ mod test {
     }
 
     #[test]
+    #[ignore] // flaky, see https://github.com/tokio-rs/tracing/issues/751
     fn logs_dropped_if_lossy() {
         let (mock_writer, rx) = MockWriter::new(1);