Compliant Checker portential issue: Check requires legacy `branch_time` even though CMIP6 uses `branch_time_in_child` / `branch_time_in_parent`

[rhaegar325]

Summary

compliance-checker --test wcrp_cmip6:1.0 reports a MED-priority failure on
every CMIP6 file we tested:

Required global attribute 'branch_time' is missing.

But CMIP6 does not require a singular branch_time global attribute. The
required CMIP6 attributes for branching are branch_time_in_child and
branch_time_in_parent, both of which are present in every failing file. The
singular branch_time was a CMIP5-era convention.

This looks like a checker / esgvoc registry asserting a legacy attribute,
producing a universal false positive on otherwise CMIP6-compliant files.

Checker Output (verbatim)

[ATTR001] Global attribute 'branch_time' existence   (weight=2)  value=[0, 1]
  Required global attribute 'branch_time' is missing.

What the Files Actually Have

CMIP6-compliant branch attributes are present and well-formed in every file:

:experiment_id           = "historical" ;
:parent_experiment_id    = "piControl" ;
:parent_activity_id      = "CMIP" ;
:parent_source_id        = "ACCESS-ESM1-5" ;
:parent_variant_label    = "r1i1p1f1" ;
:parent_time_units       = "days since 0001-01-01 00:00:00" ;
:parent_mip_era          = "CMIP6" ;
:branch_time_in_child    = 0. ;
:branch_time_in_parent   = 0. ;
:branch_method           = "standard" ;

There is no branch_time global attribute — by CMIP6 convention there
should not be.