build(deps): bump proc-macro2 from 1.0.20 to 1.0.21

Bumps [proc-macro2](https://github.com/alexcrichton/proc-macro2) from 1.0.20 to 1.0.21.
- [Release notes](https://github.com/alexcrichton/proc-macro2/releases)
- [Commits](https://github.com/alexcrichton/proc-macro2/compare/1.0.20...1.0.21)

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

Cargo.lock

@@ -1248,9 +1248,9 @@ checksum = "eba180dafb9038b050a4c280019bbedf9f2467b61e5d892dcad585bb57aadc5a"
 
 [[package]]
 name = "proc-macro2"
-version = "1.0.20"
+version = "1.0.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "175c513d55719db99da20232b06cda8bab6b83ec2d04e3283edf0213c37c1a29"
+checksum = "36e28516df94f3dd551a587da5357459d9b36d945a7c37c3557928c1c2ff2a2c"
 dependencies = [
  "unicode-xid",
 ]