OpenWrt server no longer allows http for images. As the error message says, you need to install libustream-wolfssl and ca-bundle to enable https support to wget. This requires about 1 MB of flash space. wolfssl is the smallest option if you don't already have another ssl library. If something depending on for example openssl is already installed, use libustream-openssl.
Technically you don't need ca-bundle, as you can choose not to verify the server certificate with --no-check-certificate, but that's insecure.