refinfra: update mbedtls version to v3.6.0

With the TF-A commit `55aed7d` (feat(mbedtls): update config for 3.6.0)
TF-A expects mbedTLS library to be at v3.6.0. Update the manifest to
meet this requirement.

Change-Id: I86eef7b1a0fb5295ef0f849620412a31c946182e
Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>