When investigating some Decimal128 usages in the BSON test suite, I found that the BSON corpus tests when testing extended JSON parse errors were actually passing the scenario string to Decimal128.fromString. This will always give false positives of the errors since it's the wrong function call on the wrong object.

Fixed with one line change to parse the JSON into EJSON.

PR: https://github.com/mongodb/js-bson/pull/436