Better error with leading quotes?

[samdphillips]

When setting the KEYRING env variable in Docker env file everything on the line after the = is set as the environment variable. If the user quotes the value it causes an unhelpful error message

keyring: error initializing keyring from environment
keyring: keyring spec: "\"env://?prefix=AUTH\""
keyring: make-keyring-from-string: invalid backend url;
  backend: #f
  url: "env://?prefix=AUTH"
  orig-exn: invalid URL string; bad scheme
  scheme: "\"env"
  in: "\"env://?prefix=AUTH\""