SE05x KeyID is not correctly encoded into the private key reference

[lagosantol]

The issue is in this line:

ArduinoCore-renesas/libraries/SSLClient/src/SSLClient.cpp

Line 380 in c0f158f

key[28] = KeySlot;

Only the least significant byte of the key ID is stored.
The key ID should be stored in 4 bytes, big endian.