Bump futures from 0.3.19 to 0.3.21 (#11133)

Bumps [futures](https://github.com/rust-lang/futures-rs) from 0.3.19 to 0.3.21.
- [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/0.3.19...0.3.21)

---
updated-dependencies:
- dependency-name: futures
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

substrate/client/consensus/babe/Cargo.toml

@@ -43,7 +43,7 @@ sc-consensus-slots = { version = "0.10.0-dev", path = "../slots" }
 sp-runtime = { version = "6.0.0", path = "../../../primitives/runtime" }
 fork-tree = { version = "3.0.0", path = "../../../utils/fork-tree" }
 prometheus-endpoint = { package = "substrate-prometheus-endpoint", path = "../../../utils/prometheus", version = "0.10.0-dev" }
-futures = "0.3.19"
+futures = "0.3.21"
 parking_lot = "0.12.0"
 log = "0.4.8"
 schnorrkel = { version = "0.9.1", features = ["preaudit_deprecated"] }

substrate/client/consensus/babe/rpc/Cargo.toml

@@ -23,7 +23,7 @@ serde = { version = "1.0.136", features = ["derive"] }
 sp-blockchain = { version = "4.0.0-dev", path = "../../../../primitives/blockchain" }
 sp-runtime = { version = "6.0.0", path = "../../../../primitives/runtime" }
 sc-consensus-epochs = { version = "0.10.0-dev", path = "../../epochs" }
-futures = "0.3.19"
+futures = "0.3.21"
 thiserror = "1.0"
 sp-api = { version = "4.0.0-dev", path = "../../../../primitives/api" }
 sp-consensus = { version = "0.10.0-dev", path = "../../../../primitives/consensus/common" }