build: bump rustc-demangle from 0.1.20 to 0.1.21

Bumps [rustc-demangle](https://github.com/alexcrichton/rustc-demangle) from 0.1.20 to 0.1.21.
- [Release notes](https://github.com/alexcrichton/rustc-demangle/releases)
- [Commits](https://github.com/alexcrichton/rustc-demangle/compare/0.1.20...0.1.21)

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

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

Cargo.lock

@@ -866,9 +866,9 @@ dependencies = [
 
 [[package]]
 name = "rustc-demangle"
-version = "0.1.20"
+version = "0.1.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "dead70b0b5e03e9c814bcb6b01e03e68f7c57a80aa48c72ec92152ab3e818d49"
+checksum = "7ef03e0a2b150c7a90d01faf6254c9c48a41e95fb2a8c2ac1c6f0d2b9aefc342"
 
 [[package]]
 name = "rustc_version"