ENH Replace gpuci_conda_retry with gpuci_mamba_retry

[dillon-cullinan]

mamba was recently added to gpuCI build environment, testing usage and solvability with this PR which should speed up build times.

[dillon-cullinan]

rerun tests

[codecov-commenter]

Codecov Report

Merging #675 (ae2d5aa) into branch-21.10 (ff81f0c) will increase coverage by 30.29%.
The diff coverage is 85.71%.

❗ Current head ae2d5aa differs from pull request most recent head fab8e12. Consider uploading reports for the commit fab8e12 to get more accurate results

@@                Coverage Diff                @@
##           branch-21.10     #675       +/-   ##
=================================================
+ Coverage         60.01%   90.30%   +30.29%     
=================================================
  Files                21       15        -6     
  Lines              2606     1651      -955     
=================================================
- Hits               1564     1491       -73     
+ Misses             1042      160      -882     

Impacted Files	Coverage Δ
dask_cuda/cuda_worker.py	78.31% <ø> (ø)
dask_cuda/local_cuda_cluster.py	79.41% <ø> (ø)
dask_cuda/utils.py	88.94% <85.71%> (+1.20%)	⬆️
dask_cuda/benchmarks/local_cupy_map_overlap.py
dask_cuda/_version.py
dask_cuda/benchmarks/utils.py
dask_cuda/benchmarks/local_cudf_shuffle.py
dask_cuda/benchmarks/local_cudf_merge.py
dask_cuda/benchmarks/local_cupy.py
dask_cuda/explicit_comms/dataframe/shuffle.py	98.69% <0.00%> (+0.65%)	⬆️
... and 8 more

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[dillon-cullinan]

@gpucibot merge