Bump third_party/mbedtls/repo from `a8b3d0c` to `247e6f0` (#26712)

Bumps [third_party/mbedtls/repo](https://github.com/ARMmbed/mbedtls) from `a8b3d0c` to `247e6f0`.
- [Release notes](https://github.com/ARMmbed/mbedtls/releases)
- [Commits](https://github.com/ARMmbed/mbedtls/compare/a8b3d0c7a27592ba103981a6115367a2822761bf...247e6f088dbe19e5482e038009f45210586036c9)

---
updated-dependencies:
- dependency-name: third_party/mbedtls/repo
  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/mbedtls/repo b/third_party/mbedtls/repo
index a8b3d0c..247e6f0 160000
--- a/third_party/mbedtls/repo
+++ b/third_party/mbedtls/repo
@@ -1 +1 @@
-Subproject commit a8b3d0c7a27592ba103981a6115367a2822761bf
+Subproject commit 247e6f088dbe19e5482e038009f45210586036c9