Fixes the following error when testing against a compiler older
than 1.64:
error: failed to select a version for the requirement `hashbrown = "^0.14"`
candidate versions found which didn't match: 0.13.2, 0.13.1, 0.12.3, ...
location searched: crates.io index
required by package `indexmap v2.0.0`
... which satisfies dependency `indexmap = "^2"` of package `serde_json v1.0.97`
... which satisfies path dependency `serde_json` of package `serde_json_test v0.0.0`
