build: Bump darling from 0.20.3 to 0.20.6

Bumps [darling](https://github.com/TedDriggs/darling) from 0.20.3 to 0.20.6.
- [Release notes](https://github.com/TedDriggs/darling/releases)
- [Changelog](https://github.com/TedDriggs/darling/blob/master/CHANGELOG.md)
- [Commits](https://github.com/TedDriggs/darling/compare/v0.20.3...v0.20.6)

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

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

Cargo.lock

@@ -534,9 +534,9 @@ dependencies = [
 
 [[package]]
 name = "darling"
-version = "0.20.3"
+version = "0.20.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0209d94da627ab5605dcccf08bb18afa5009cfbef48d8a8b7d7bdbc79be25c5e"
+checksum = "c376d08ea6aa96aafe61237c7200d1241cb177b7d3a542d791f2d118e9cbb955"
 dependencies = [
  "darling_core",
  "darling_macro",
@@ -544,9 +544,9 @@ dependencies = [
 
 [[package]]
 name = "darling_core"
-version = "0.20.3"
+version = "0.20.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "177e3443818124b357d8e76f53be906d60937f0d3a90773a664fa63fa253e621"
+checksum = "33043dcd19068b8192064c704b3f83eb464f91f1ff527b44a4e2b08d9cdb8855"
 dependencies = [
  "fnv",
  "ident_case",
@@ -558,9 +558,9 @@ dependencies = [
 
 [[package]]
 name = "darling_macro"
-version = "0.20.3"
+version = "0.20.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "836a9bbc7ad63342d6d6e7b815ccab164bc77a2d95d84bc3117a8c0d5c98e2d5"
+checksum = "c5a91391accf613803c2a9bf9abccdbaa07c54b4244a5b64883f9c3c137c86be"
 dependencies = [
  "darling_core",
  "quote",