Bump proc-macro2 from 1.0.67 to 1.0.68 (#3363)

Bumps [proc-macro2](https://github.com/dtolnay/proc-macro2) from 1.0.67 to 1.0.68.
- [Release notes](https://github.com/dtolnay/proc-macro2/releases)
- [Commits](https://github.com/dtolnay/proc-macro2/compare/1.0.67...1.0.68)

---
updated-dependencies:
- dependency-name: proc-macro2
  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>

Cargo.lock

@@ -2252,9 +2252,9 @@ dependencies = [
 
 [[package]]
 name = "proc-macro2"
-version = "1.0.67"
+version = "1.0.68"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3d433d9f1a3e8c1263d9456598b16fec66f4acc9a74dacffd35c7bb09b3a1328"
+checksum = "5b1106fec09662ec6dd98ccac0f81cef56984d0b49f75c92d8cbad76e20c005c"
 dependencies = [
  "unicode-ident",
 ]