Update flume requirement from 0.11 to 0.12

Updates the requirements on [flume](https://github.com/zesterer/flume) to permit the latest version.
- [Changelog](https://github.com/zesterer/flume/blob/master/CHANGELOG.md)
- [Commits](https://github.com/zesterer/flume/commits)

---
updated-dependencies:
- dependency-name: flume
  dependency-version: 0.12.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

Cargo.toml

@@ -26,7 +26,7 @@ portable-atomic = { version = "1", optional = true, default-features = false }
 atomic-waker = "1"
 easy-parallel = "3"
 flaky_test = "0.2"
-flume = { version = "0.11", default-features = false }
+flume = { version = "0.12", default-features = false }
 futures-lite = "2.0.0"
 once_cell = "1"
 pin-project-lite = "0.2.10"