test: fix CDC partial update checker schema (#49993)

## What this PR does

Fixes CDC stability checker initialization for partial update.

The shared CDC chaos checker schema includes struct-array fields.
PyMilvus rejects `partial_update=True` when the collection schema
contains struct fields, so `PartialUpdateChecker` should not be
initialized with the shared collection name and shared struct schema.

This PR keeps the master all-datatype schema intact for the other
checkers, including struct-array fields, BM25, MinHash, and nullable
settings. Only `PartialUpdateChecker` gets its own schema with
`enable_struct_array_field=False` and its own collection:

- shared checkers: `_build_checker_schema()`
- partial update checker:
`_build_checker_schema(enable_struct_array_field=False)` and no shared
`collection_name`

## Tests

- `uv run python -m py_compile
cdc/stablity/test_single_request_operation.py`
- `uvx ruff@0.15.11 check
tests/python_client/cdc/stablity/test_single_request_operation.py`
- `uvx ruff@0.15.11 format --check --diff
tests/python_client/cdc/stablity/test_single_request_operation.py`
- Local schema check: shared schema keeps
`struct_fields=["array_struct"]`, BM25, and MinHash; partial-update
schema has `struct_fields=[]` while still keeping BM25 and MinHash

Signed-off-by: zhuwenxing <wenxing.zhu@zilliz.com>