Bump third_party/mbedtls/repo from 4637ed2 to 4afd4b9

Bumps [third_party/mbedtls/repo](https://github.com/ARMmbed/mbedtls) from `4637ed2` to `4afd4b9`.
- [Release notes](https://github.com/ARMmbed/mbedtls/releases)
- [Commits](Mbed-TLS/mbedtls@4637ed2...4afd4b9)

---
updated-dependencies:
- dependency-name: third_party/mbedtls/repo
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>