GHSA-2JCC-MXV7-P3F9 oasdiff does not enforce --allow-external-refs=false on the git-revision load path (SSRF / local file read)

Summary From v1.13.2 through v1.18.0, oasdiff did not enforce --allow-external-refs=false library: openapi3.Loader.IsExternalRefsAllowed = false when loading a spec from a git revision the rev:path form, e.g. main:openapi.yaml. External $refs were resolved on that load path even when external ref...