Bump thiserror from 2.0.20 to 2.0.21 in /divviup/rust - #605

Failed to generate-and-submit dependency graph. Will continue. HttpError: Dependency submission failed for dependency-graph-reports/ci-build.json. Resource not accessible by integration - https://docs.github.com/rest/dependency-graph/dependency-submission#create-a-snapshot-of-dependencies-for-a-repository