message: chore: ignore flaky field filter tests
  This branch changes the `field_filter_events` and `field_filter_spans`
  tests in `tracing-subscriber` to be ignored by default, as they often
  fail spuriously on CI.
  The tests can still be run using
  ```shell
  $ RUSTFLAGS="--cfg flaky_tests" cargo test
  ```
  or similar.
diff: @@ -4,6 +4,7 @@ use tracing::{self, collect::with_default, Level};
  use tracing_subscriber::{filter::EnvFilter, prelude::*};
  #[test]
  +#[cfg_attr(not(flaky_tests), ignore)]
  fn field_filter_events() {
  let filter: EnvFilter = "[{thing}]=debug".parse().expect("filter should parse");
  let (subscriber, finished) = collector::mock()
  @@ -33,6 +34,7 @@ fn field_filter_events() {
  }
  #[test]
  +#[cfg_attr(not(flaky_tests), ignore)]
  fn field_filter_spans() {
  let filter: EnvFilter = "[{enabled=true}]=debug"
  .parse()
  