Bump third_party/yaml-cpp from `33316d5` to `a6bbe0e`

Bumps [third_party/yaml-cpp](https://github.com/jbeder/yaml-cpp) from `33316d5` to `a6bbe0e`.
- [Release notes](https://github.com/jbeder/yaml-cpp/releases)
- [Commits](https://github.com/jbeder/yaml-cpp/compare/33316d531bd9032d66f5bcc3ba1fd114a4ab0e1c...a6bbe0e50ac4074f0b9b44188c28cf00caf1a723)

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

third_party/yaml-cpp

diff --git a/third_party/yaml-cpp b/third_party/yaml-cpp
index 33316d5..a6bbe0e 160000
--- a/third_party/yaml-cpp
+++ b/third_party/yaml-cpp
@@ -1 +1 @@
-Subproject commit 33316d531bd9032d66f5bcc3ba1fd114a4ab0e1c
+Subproject commit a6bbe0e50ac4074f0b9b44188c28cf00caf1a723