jv: validation fails with YAML input with timestamps

[andrewpollock]

$ jv --version
github.com/santhosh-tekuri/jsonschema/cmd/jv v0.7.0
github.com/santhosh-tekuri/jsonschema/v6 v6.0.1
github.com/spf13/pflag v1.0.5
golang.org/x/text v0.14.0
gopkg.in/yaml.v3 v3.0.1

Validating https://raw.githubusercontent.com/pypa/advisory-database/70de06387b0406a6b9a44f62870ba3cec9642993/vulns/aiocpa/PYSEC-2024-152.yaml seems to be failing unexpectedly:

 ~/go/bin/jv https://raw.githubusercontent.com/ossf/osv-schema/main/validation/schema.json aiocpa/PYSEC-2024-152.yaml 
schema https://raw.githubusercontent.com/ossf/osv-schema/main/validation/schema.json: ok

instance aiocpa/PYSEC-2024-152.yaml: failed
jsonschema validation failed with 'https://raw.githubusercontent.com/ossf/osv-schema/main/validation/schema.json#'
- at '/modified': invalid jsonType time.Time

[andrewpollock]

/cc @di FYI

[santhosh-tekuri]

yaml package does not provide any way to decode timestamps as strings. so it might require special conversions to string during validation phase.