build(deps): bump third_party/abseil-cpp from `688dd51` to `51b7426` (#2478)

Bumps [third_party/abseil-cpp](https://github.com/abseil/abseil-cpp) from `688dd51` to `51b7426`.
- [Release notes](https://github.com/abseil/abseil-cpp/releases)
- [Commits](https://github.com/abseil/abseil-cpp/compare/688dd51cc48f9d4dafeaab87e10bc7c0e4a3ecb6...51b7426e922d2f00f82117f030f40e767af5901b)

---
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 688dd51..51b7426 160000
--- a/third_party/abseil-cpp
+++ b/third_party/abseil-cpp
@@ -1 +1 @@
-Subproject commit 688dd51cc48f9d4dafeaab87e10bc7c0e4a3ecb6
+Subproject commit 51b7426e922d2f00f82117f030f40e767af5901b