mbedtls: security bump to version 2.28.7

mbedtls: security bump to version 2.28.7

This release of Mbed TLS provides bug fixes and minor enhancements. This
release includes fixes for following security issues:

* Timing side channel in private key RSA operations (CVE-2024-23170)

  Mbed TLS is vulnerable to a timing side channel in private key RSA
  operations. This side channel could be sufficient for an attacker to
  recover the plaintext. A local attacker or a remote attacker who is
  close to the victim on the network might have precise enough timing
  measurements to exploit this. It requires the attacker to send a large
  number of messages for decryption.

* Buffer overflow in mbedtls_x509_set_extension() (CVE-2024-23775)

  When writing x509 extensions we failed to validate inputs passed in to
  mbedtls_x509_set_extension(), which could result in an integer overflow,
  causing a zero-length buffer to be allocated to hold the extension. The
  extension would then be copied into the buffer, causing a heap buffer
  overflow.

Fixes: CVE-2024-23170, CVE-2024-23775
References: https://mbed-tls.readthedocs.io/en/latest/security-advisories/mbedtls-security-advisory-2024-01-1/
References: https://mbed-tls.readthedocs.io/en/latest/security-advisories/mbedtls-security-advisory-2024-01-2/
Signed-off-by: orangepizza <tjtncks@gmail.com>
Signed-off-by: Petr Štetiar <ynezz@true.cz> [formal fixes]