[Fix] Fix warning with torch.meshgrid.

[pallgeuer]

Motivation

torch.meshgrid() has started raising a warning when not called with an explicit indexing parameter:
https://pytorch.org/docs/stable/generated/torch.meshgrid.html

Modification

Provide indexing='ij' to all calls to torch.meshgrid that don't already specify indexing.

Checklist

Before PR:

• Pre-commit or other linting tools are used to fix the potential lint issues.
• Bug fixes are fully covered by unit tests, the case that causes the bug should be added in the unit tests.
• The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• The documentation has been modified accordingly, like docstring or example tutorials.

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with those projects, like MMDet or MMSeg.
• CLA has been signed and all committers have signed the CLA in this PR.

[CLAassistant]

All committers have signed the CLA.

[pallgeuer]

Refer to open-mmlab/mmdetection#8090 (comment) for discussion on PyTorch version support of torch.meshgrid.

[pallgeuer]

I have updated the PR with the same solution as used for mmpose and mmdet. This should be ready to merge now.

[codecov]

Codecov Report

Base: 86.80% // Head: 85.39% // Decreases project coverage by -1.41% ⚠️

Coverage data is based on head (c106dc1) compared to base (877ea30).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #860      +/-   ##
==========================================
- Coverage   86.80%   85.39%   -1.42%     
==========================================
  Files         130      134       +4     
  Lines        8571     8775     +204     
  Branches     1478     1435      -43     
==========================================
+ Hits         7440     7493      +53     
- Misses        909     1058     +149     
- Partials      222      224       +2     

Flag	Coverage Δ
unittests	85.33% <ø> (-1.39%)	⬇️

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

Impacted Files	Coverage Δ
mmcls/utils/setup_env.py	95.45% <0.00%> (-4.55%)	⬇️
mmcls/datasets/builder.py	83.78% <0.00%> (-4.06%)	⬇️
mmcls/apis/train.py	15.38% <0.00%> (-0.53%)	⬇️
mmcls/utils/__init__.py	100.00% <0.00%> (ø)
mmcls/core/hook/__init__.py	100.00% <0.00%> (ø)
mmcls/core/evaluation/__init__.py	100.00% <0.00%> (ø)
mmcls/utils/distribution.py	10.52% <0.00%> (ø)
mmcls/core/hook/wandblogger_hook.py	18.57% <0.00%> (ø)
mmcls/core/evaluation/eval_hooks.py	28.94% <0.00%> (ø)
mmcls/utils/device.py	100.00% <0.00%> (ø)
... and 2 more

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