Update dask_cudf imports to be compatible with latest dask

[rlratzel]

Updated imports to be compatible with latest dask after dask/dask#8796
This change is also compatible with dask versions prior to the above dask PR.

Tested import dask_cudf with both dask 2022.02.2a220314 and 2022.02.2a220315.

[codecov]

Codecov Report

Merging #10442 (806540c) into branch-22.04 (4596244) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@               Coverage Diff                @@
##           branch-22.04   #10442      +/-   ##
================================================
+ Coverage         86.13%   86.18%   +0.04%     
================================================
  Files               139      139              
  Lines             22438    22468      +30     
================================================
+ Hits              19328    19363      +35     
+ Misses             3110     3105       -5     

Impacted Files	Coverage Δ
python/cudf/cudf/core/tools/numeric.py	89.24% <100.00%> (+0.11%)	⬆️
python/dask_cudf/dask_cudf/backends.py	86.44% <100.00%> (+1.47%)	⬆️
...ython/dask_cudf/dask_cudf/io/tests/test_parquet.py	100.00% <100.00%> (ø)
python/cudf/cudf/core/column/string.py	88.39% <0.00%> (+0.12%)	⬆️
python/cudf/cudf/core/groupby/groupby.py	91.57% <0.00%> (+0.22%)	⬆️
python/cudf/cudf/core/column/numerical.py	95.28% <0.00%> (+0.29%)	⬆️
python/cudf/cudf/core/tools/datetimes.py	84.49% <0.00%> (+0.30%)	⬆️
python/cudf/cudf/core/column/lists.py	90.56% <0.00%> (+0.47%)	⬆️

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[shwina]

@gpucibot merge