[CI] Fix CI for timm, pycocotools, onnx

[shinya7y]

Modification

1. Remove timm from requirements/optional.txt like Fix CircleCI and readthedoc build failed #8980 because timm v0.6.11 requires torch>=1.7 and breaks CI.
   Another possible way to fix this issue: [CI] fix timm related bug for master mmaction2#1975
2. Fix CI for pycocotools by setting CFLAGS like [Fix] pycocotools install fail  mmaction2#1831 and fix cuda ci of building lanms-neo mmdeploy#945
3. Fix CI for onnx by setting CXXFLAGS

For 2. and 3., a more direct cause of behavioral change in GitHub Actions may be related to actions/setup-python#485 and actions/setup-python#507 .

[codecov]

Codecov Report

Base: 64.05% // Head: 64.19% // Increases project coverage by +0.13% 🎉

Coverage data is based on head (32ba811) compared to base (a502d8f).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #9034      +/-   ##
==========================================
+ Coverage   64.05%   64.19%   +0.13%     
==========================================
  Files         361      361              
  Lines       29538    29543       +5     
  Branches     4921     5023     +102     
==========================================
+ Hits        18922    18964      +42     
+ Misses       9596     9570      -26     
+ Partials     1020     1009      -11     

Flag	Coverage Δ
unittests	64.16% <ø> (+0.10%)	⬆️

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

Impacted Files	Coverage Δ
mmdet/datasets/samplers/infinite_sampler.py	24.69% <0.00%> (-0.63%)	⬇️
mmdet/datasets/custom.py	61.45% <0.00%> (+0.20%)	⬆️
mmdet/datasets/pipelines/transforms.py	76.00% <0.00%> (+0.52%)	⬆️
mmdet/models/dense_heads/corner_head.py	69.72% <0.00%> (+1.38%)	⬆️
mmdet/core/bbox/samplers/sampling_result.py	74.60% <0.00%> (+1.58%)	⬆️
mmdet/models/roi_heads/test_mixins.py	52.85% <0.00%> (+2.14%)	⬆️
mmdet/utils/misc.py	64.44% <0.00%> (+2.22%)	⬆️
mmdet/models/dense_heads/dense_test_mixins.py	43.20% <0.00%> (+2.46%)	⬆️
mmdet/core/bbox/assigners/sim_ota_assigner.py	83.63% <0.00%> (+3.63%)	⬆️
mmdet/models/detectors/cornernet.py	100.00% <0.00%> (+5.12%)	⬆️
... and 3 more

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