[MAINTENANCE] Assert store access in DatasourceDict just-in-time tests

[anxkhn]

Two unit tests in tests/datasource/test_datasource_dict.py that are meant to verify DatasourceDict reads its store just-in-time were not asserting anything, so they passed unconditionally and gave no regression protection.

• test_datasource_dict_data_property_requests_store_just_in_time
• test_datasource_dict___contains___requests_store_just_in_time

Both wrote:

store.list_keys_count = 0
_ = empty_datasource_dict.data
store.list_keys_count = 1

Lines 100/102 (and 111/113 in the second test) are plain assignments to the spy counter, not assertions, so nothing is ever checked. Every other test in the same file uses the assert store.<counter> == N pattern (for example assert store.set_count == 1).

Root cause

Two problems compound:

1. = was written where assert ... == was intended, so the tests assert nothing.
2. The counter is the wrong one. DatasourceDict.data (great_expectations/datasource/datasource_dict.py:71) calls self._datasource_store.get_all(), not list_keys(). DatasourceStoreSpy tracks get/set/list_keys/has_key/remove_key but does not override get_all, so list_keys_count stays 0 on a .data access. Even the naive repair (assert store.list_keys_count == 1) would fail.

The behavior these tests are named for is documented at great_expectations/datasource/datasource_dict.py:63-67:

This is generated just-in-time as the contents of the store may have changed.

Fix

Have the spy track get_all() and assert on it, so both tests become real red -> green guards for just-in-time store access:

• Add get_all_count to DatasourceStoreSpy (initialized in __init__ and reset alongside the existing counters) and override get_all() to increment it via super().get_all(), matching the file's existing spy-override style.
• Replace the four assignment lines with assert store.get_all_count == 0 before the .data access and assert store.get_all_count == 1 after.

Testing

• python -m pytest tests/datasource/test_datasource_dict.py -q -> 13 passed.
• Red -> green check: temporarily making .data skip the store makes both tests fail with assert 0 == 1; reverting restores green. Before this change they passed against that same breakage.
• invoke lint --path tests/datasource/test_datasource_dict.py passes (import-sort, ruff format --check, ruff check).

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PR checklist (from the repo template)

• Description of PR changes above includes a link to an existing GitHub issue
  -- see note below; no matching issue exists, and recent test-harness [MAINTENANCE] PRs merged without one.
• PR title is prefixed with one of: [BUGFIX], [FEATURE], [DOCS], [MAINTENANCE], [CONTRIB], [MINORBUMP]
• Code is linted - run invoke lint (uses ruff format + ruff check)
• Appropriate tests and docs have been updated

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