Plugin error: [proto: cannot parse invalid wire-format data]

Might be an exotic use-case due to these factors:
1. Gnostic is running in a docker container
2. The input OpenAPI spec file is on a mounted bind volume
3. Only happens with the gnostic-grpc plugin, the gnostic-text plugin works 100% okay even within the above circumstances.

Logs

```sh
Errors reading /local/packages/cactus-plugin-keychain-vault/src/main/json/openapi.json
Plugin error: [proto: cannot parse invalid wire-format data]

```

To reproduce

1. Run the containerized gnostic that was built from this [Dockerfile](https://github.com/petermetz/cactus/blob/gnostic-repro-steps-docker-volumes/tools/docker/gnostic/Dockerfile)

```sh
git clone https://github.com/petermetz/cactus.git
cd cactus
git checkout gnostic-repro-steps-docker-volumes

docker run --rm -it --mount type=bind,src=$(pwd),dst=/local/ petermetz/cactus-gnostic bash

gnostic /local/packages/cactus-plugin-keychain-vault/src/main/json/openapi.json --grpc-out=/tmp/
# this fails with the error shown above in the logs section

cp /local/packages/cactus-plugin-keychain-vault/src/main/json/openapi.json /tmp/
# this succeeds
gnostic /tmp/openapi.json --grpc-out=/tmp/

```