[REVIEW] Fix Codecov.io Coverage Upload for Branch Builds

[mdemoret-nv]

Testing the following undocumented option:

codecov:
  allow_coverage_offsets: true

Suggested by Codecov.io support here to fix the linked issue with missing base reports.

[mdemoret-nv]

rerun tests

[codecov-io]

Codecov Report

Merging #3524 (c1bdcb4) into branch-0.19 (39c7262) will increase coverage by 7.56%.
The diff coverage is 71.72%.

@@               Coverage Diff               @@
##           branch-0.19    #3524      +/-   ##
===============================================
+ Coverage        71.77%   79.34%   +7.56%     
===============================================
  Files              212      225      +13     
  Lines            17075    17946     +871     
===============================================
+ Hits             12256    14239    +1983     
+ Misses            4819     3707    -1112     

Flag	Coverage Δ
dask	44.12% <14.67%> (?)
non-dask	71.62% <69.97%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...on/cuml/_thirdparty/sklearn/preprocessing/_data.py	63.61% <ø> (+0.07%)	⬆️
python/cuml/experimental/explainer/common.py	88.05% <42.85%> (-4.01%)	⬇️
...l/_thirdparty/sklearn/preprocessing/_imputation.py	62.40% <50.00%> (-0.11%)	⬇️
python/cuml/neighbors/nearest_neighbors.pyx	92.43% <50.00%> (-0.29%)	⬇️
python/cuml/neighbors/ann.pyx	61.62% <61.62%> (ø)
python/cuml/common/import_utils.py	59.43% <66.66%> (+3.43%)	⬆️
python/cuml/experimental/explainer/base.pyx	67.06% <67.06%> (ø)
python/cuml/dask/common/utils.py	43.68% <83.33%> (+16.13%)	⬆️
python/cuml/experimental/explainer/kernel_shap.pyx	97.75% <100.00%> (+0.48%)	⬆️
...n/cuml/experimental/explainer/permutation_shap.pyx	98.82% <100.00%> (+0.84%)	⬆️
... and 71 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 430593d...c1bdcb4. Read the comment docs.

[mdemoret-nv]

Changing this PRs focus from fixing the missing base report to fixing coverage upload for branch builds. Branch build coverage will be necessary to fix missing base reports. Therefore this PR needs to be merged before we can see any effect.

[JohnZed]

LGTM

[JohnZed]

@gpucibot merge