Yes, this is one of the issues bugging me to quite often.

Within the
environment you'll also need to run:

export SSL_CERT_DIR="$GUIX_ENVIRONMENT/etc/ssl/certs"
export SSL_CERT_FILE="$GUIX_ENVIRONMENT/etc/ssl/certs/ca-certificates.crt"
export GIT_SSL_CAINFO="$SSL_CERT_FILE"

(This is why I wrote myself a script for setting up a guix environment.)