Bump pandas to 2.0 in mindeps build

[jrbourbeau]

dask.dataframe recently bumped it's minimum pandas version to 2.0. I noticed some related failures here (for example, this CI build) in our mindeps-pandas CI build.

This PR bumps the pandas in the mindeps build to 2.0

[jrbourbeau]

We were still getting this error due to dask-expr not being installed

_________________________________________________________________________________ ERROR collecting distributed/protocol/tests/test_highlevelgraph.py __________________________________________________________________________________
../../../mambaforge/envs/distributed-mindeps-pandas/lib/python3.9/site-packages/dask/dataframe/__init__.py:33: in _dask_expr_enabled
    import dask_expr  # noqa: F401
E   ModuleNotFoundError: No module named 'dask_expr'

During handling of the above exception, another exception occurred:
distributed/protocol/tests/test_highlevelgraph.py:14: in <module>
    import dask.dataframe as dd
../../../mambaforge/envs/distributed-mindeps-pandas/lib/python3.9/site-packages/dask/dataframe/__init__.py:108: in <module>
    if _dask_expr_enabled():
../../../mambaforge/envs/distributed-mindeps-pandas/lib/python3.9/site-packages/dask/dataframe/__init__.py:42: in _dask_expr_enabled
    warnings.warn(msg, FutureWarning)
E   FutureWarning:
E   Dask dataframe query planning is disabled because dask-expr is not installed.
E
E   You can install it with `pip install dask[dataframe]` or `conda install dask`.
E   This will raise in a future version.

Converting import dask.dataframe as dd to dd = pytest.importorskip("dask.dataframe") fixed things locally.

[github-actions]

Unit Test Results

See test report for an extended history of previous test failures. This is useful for diagnosing flaky tests.

    29 files  ±    0      29 suites  ±0   11h 18m 46s ⏱️ + 40m 0s
 4 083 tests ±    0   3 963 ✅  -     1    112 💤 +  7   8 ❌ +2 
55 230 runs  +3 815  52 787 ✅ +3 684  2 432 💤 +144  11 ❌ +3 

For more details on these failures, see this check.

Results for commit ce30558. ± Comparison against base commit 63e5108.

This pull request skips 8 and un-skips 1 tests.

distributed.protocol.tests.test_highlevelgraph
distributed.protocol.tests.test_pandas
distributed.shuffle.tests.test_graph
distributed.shuffle.tests.test_merge
distributed.shuffle.tests.test_merge_column_and_index
distributed.shuffle.tests.test_shuffle
distributed.shuffle.tests.test_shuffle_plugins
distributed.tests.test_dask_collections

distributed.tests.test_client ‑ test_computation_object_code_not_available