test-server: bump generated selsigned cert to 2048 bits
test-server: bump generated selsigned cert to 2048 bits

On Ubuntu 20.04 Focal, openssl is configured by default to reject the old 1024-bit keys
sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets