docs(prerequisites): update mbedtls to version 3.6.2

This new update to the LTS branch of MbedTLS provides
the fix for a buffer underrun vulnerability. TF-A does
not use the previously vulnerable functions
`mbedtls_pk_write_key_der` or `mbedtls_pk_write_key_pem`.
Full patch notes to this MbedTLS update can be found at
https://github.com/Mbed-TLS/mbedtls/releases/tag/mbedtls-3.6.2.

Change-Id: Ibc4a8712c92019648fe0e75390cd3540d86b735d
Signed-off-by: Ryan Everett <ryan.everett@arm.com>
1 file changed