[receiver-mock] Set opentelemetry-proto version to match the Sumo Logic receiver's version

To make sure that the tests check actual situations, we should set the proto's version to match the one used by Sumo Logic backend.
Proto will be released as a crate in the next, v0.18 release, according to a comment from an issue from the opentelemetry-rust repository. Earlier releases will probably not be supported, since proto crate didn't exist in v0.17 and earlier.

sumologic-kubernetes-tools/src/rust/receiver-mock/Cargo.toml

Line 26 in c385cda

    
           opentelemetry-proto = { git = "https://github.com/open-telemetry/opentelemetry-rust", features = ["gen-tonic", "build-server", "logs", "metrics"] }