Bump third_party/mbedtls/repo from 5bc604f to 2153b1b

Bumps [third_party/mbedtls/repo](https://github.com/ARMmbed/mbedtls) from `5bc604f` to `2153b1b`.
- [Release notes](https://github.com/ARMmbed/mbedtls/releases)
- [Commits](Mbed-TLS/mbedtls@5bc604f...2153b1b)

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

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Author: dependabot[bot]