Bump futures-executor from 0.3.18 to 0.3.21

Bumps [futures-executor](https://github.com/rust-lang/futures-rs) from 0.3.18 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/0.3.18...0.3.21)

---
updated-dependencies:
- dependency-name: futures-executor
  dependency-type: indirect
  update-type: version-update:semver-patch
...

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

Cargo.lock

@@ -506,9 +506,9 @@ dependencies = [
 
 [[package]]
 name = "futures-channel"
-version = "0.3.18"
+version = "0.3.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7fc8cd39e3dbf865f7340dce6a2d401d24fd37c6fe6c4f0ee0de8bfca2252d27"
+checksum = "c3083ce4b914124575708913bca19bfe887522d6e2e6d0952943f5eac4a74010"
 dependencies = [
  "futures-core",
  "futures-sink",
@@ -516,15 +516,15 @@ dependencies = [
 
 [[package]]
 name = "futures-core"
-version = "0.3.18"
+version = "0.3.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "629316e42fe7c2a0b9a65b47d159ceaa5453ab14e8f0a3c5eedbb8cd55b4a445"
+checksum = "0c09fd04b7e4073ac7156a9539b57a484a8ea920f79c7c675d05d289ab6110d3"
 
 [[package]]
 name = "futures-executor"
-version = "0.3.18"
+version = "0.3.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7b808bf53348a36cab739d7e04755909b9fcaaa69b7d7e588b37b6ec62704c97"
+checksum = "9420b90cfa29e327d0429f19be13e7ddb68fa1cccb09d65e5706b8c7a749b8a6"
 dependencies = [
  "futures-core",
  "futures-task",
@@ -533,15 +533,15 @@ dependencies = [
 
 [[package]]
 name = "futures-io"
-version = "0.3.18"
+version = "0.3.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e481354db6b5c353246ccf6a728b0c5511d752c08da7260546fc0933869daa11"
+checksum = "fc4045962a5a5e935ee2fdedaa4e08284547402885ab326734432bed5d12966b"
 
 [[package]]
 name = "futures-macro"
-version = "0.3.18"
+version = "0.3.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a89f17b21645bc4ed773c69af9c9a0effd4a3f1a3876eadd453469f8854e7fdd"
+checksum = "33c1e13800337f4d4d7a316bf45a567dbcb6ffe087f16424852d97e97a91f512"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -550,21 +550,21 @@ dependencies = [
 
 [[package]]
 name = "futures-sink"
-version = "0.3.18"
+version = "0.3.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "996c6442437b62d21a32cd9906f9c41e7dc1e19a9579843fad948696769305af"
+checksum = "21163e139fa306126e6eedaf49ecdb4588f939600f0b1e770f4205ee4b7fa868"
 
 [[package]]
 name = "futures-task"
-version = "0.3.18"
+version = "0.3.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "dabf1872aaab32c886832f2276d2f5399887e2bd613698a02359e4ea83f8de12"
+checksum = "57c66a976bf5909d801bbef33416c41372779507e7a6b3a5e25e4749c58f776a"
 
 [[package]]
 name = "futures-util"
-version = "0.3.18"
+version = "0.3.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "41d22213122356472061ac0f1ab2cee28d2bac8491410fd68c2af53d1cedb83e"
+checksum = "d8b7abd5d659d9b90c8cba917f6ec750a74e2dc23902ef9cd4cc8c8b22e6036a"
 dependencies = [
  "futures-channel",
  "futures-core",