Disable .env files in direnv.

direnv started using either .envrc or .env files. I've a bunch of .env
files (mainly for setting the project name in Docker Compose) and I
don't want to set them in the shell nor have the annoying warning
everytime I cd to a directory. Set the old behavior back.

.config/direnv/direnv.toml

+[global]
+skip_dotenv = true