Bump third_party/mbedtls/repo from da635ab to d6d43ec (#30277)

Bumps [third_party/mbedtls/repo](https://github.com/ARMmbed/mbedtls) from `da635ab` to `d6d43ec`.
- [Release notes](https://github.com/ARMmbed/mbedtls/releases)
- [Commits](Mbed-TLS/mbedtls@da635ab...d6d43ec)

---
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>
Co-authored-by: Andrei Litvin <andy314@gmail.com>

Author: dependabot[bot]