build(deps): bump third_party/yaml-cpp from `b11eaf1` to `84459a7` (#2410)

Bumps [third_party/yaml-cpp](https://github.com/jbeder/yaml-cpp) from `b11eaf1` to `84459a7`.
- [Release notes](https://github.com/jbeder/yaml-cpp/releases)
- [Commits](https://github.com/jbeder/yaml-cpp/compare/b11eaf16310d3ceab04db3d07dd3f90b05a661a5...84459a7f982ea4d10e943237b2e9c71afdab6a45)

---
updated-dependencies:
- dependency-name: third_party/yaml-cpp
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
diff --git a/third_party/yaml-cpp b/third_party/yaml-cpp
index b11eaf1..84459a7 160000
--- a/third_party/yaml-cpp
+++ b/third_party/yaml-cpp
@@ -1 +1 @@
-Subproject commit b11eaf16310d3ceab04db3d07dd3f90b05a661a5
+Subproject commit 84459a7f982ea4d10e943237b2e9c71afdab6a45