Fix yield statement in test_get_custody_columns

[jtraglia]

We noticed this error during test generation:

ruamel.yaml.representer.RepresenterError: cannot represent an object: 128

consensus-specs/tests/core/pyspec/eth2spec/test/eip7594/networking/test_get_custody_columns.py

Line 19 in dbc746f

yield 'custody_subnet_count', 'meta', custody_subnet_count

Called here:

consensus-specs/tests/core/pyspec/eth2spec/test/eip7594/networking/test_get_custody_columns.py

Lines 44 to 46 in dbc746f

	yield from _run_get_custody_columns(
	spec, rng, node_id=0,
	custody_subnet_count=spec.config.DATA_COLUMN_SIDECAR_SUBNET_COUNT)

This was happening because we changed the type of DATA_COLUMN_SIDECAR_SUBNET_COUNT to uint64.

consensus-specs/specs/_features/eip7594/das-core.md

Line 70 in 423bb4d

| `DATA_COLUMN_SIDECAR_SUBNET_COUNT` | `128` | The number of data column sidecar subnets used in the gossipsub protocol |

consensus-specs/specs/_features/eip7594/das-core.md

Line 70 in dbc746f

| `DATA_COLUMN_SIDECAR_SUBNET_COUNT` | `uint64(128)` | The number of data column sidecar subnets used in the gossipsub protocol |

The solution is to cast this to a native int type that ruamel understands.