It is my understanding that the specs repo does not currently have an extended json v1 corpus, since it was in-place replaced by the extended json v2 corpus. But, since the Ruby driver implemented extended json v1, it did have the respective corpus tests.

✅Restore https://github.com/mongodb/bson-ruby/tree/v4.7.0/spec/support/corpus-tests as spec/spec_tests/data/corpus_legacy.
Implement a test runner for this legacy corpus. I expect it to need to use

when serializing.
Verify all of the legacy corpus tests as were present in bson 4.7.0 still pass in bson master.
Consider updating the legacy corpus to https://github.com/mongodb/specifications/tree/e0d212d1fbe2a2c5d1a82216f1e89ed4f293ff2e/source/bson-corpus/tests which is the version immediately before extended json v2 merge.