build(deps): bump third_party/abseil-cpp from `3de434a` to `688dd51` (#2475)

Bumps [third_party/abseil-cpp](https://github.com/abseil/abseil-cpp) from `3de434a` to `688dd51`.
- [Release notes](https://github.com/abseil/abseil-cpp/releases)
- [Commits](https://github.com/abseil/abseil-cpp/compare/3de434ab4c0e4aee9386eb70e4418a621ad24d4c...688dd51cc48f9d4dafeaab87e10bc7c0e4a3ecb6)

---
updated-dependencies:
- dependency-name: third_party/abseil-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/abseil-cpp b/third_party/abseil-cpp
index 3de434a..688dd51 160000
--- a/third_party/abseil-cpp
+++ b/third_party/abseil-cpp
@@ -1 +1 @@
-Subproject commit 3de434ab4c0e4aee9386eb70e4418a621ad24d4c
+Subproject commit 688dd51cc48f9d4dafeaab87e10bc7c0e4a3ecb6