Bump third_party/mbedtls/repo from 83faeca to b76bcfb (#26123)

Bumps [third_party/mbedtls/repo](https://github.com/ARMmbed/mbedtls) from `83faeca` to `b76bcfb`.
- [Release notes](https://github.com/ARMmbed/mbedtls/releases)
- [Commits](Mbed-TLS/mbedtls@83faeca...b76bcfb)

---
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>