Bump futures-executor from 0.3.5 to 0.3.8
Bump futures-executor from 0.3.5 to 0.3.8

Bumps [futures-executor](https://github.com/rust-lang/futures-rs) from 0.3.5 to 0.3.8.
- [Release notes](https://github.com/rust-lang/futures-rs/releases)
- [Changelog](https://github.com/rust-lang/futures-rs/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rust-lang/futures-rs/compare/0.3.5...0.3.8)

Signed-off-by: dependabot-preview[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
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