Upgrade PT to 1.9.0 in unit-test

[zhiqwang]

To simplify the unit-tests, we upgraded the PT to 1.9.0, but the core functionality of this package is workable on PT 1.7.0 and above.

[codecov]

Codecov Report

Merging #161 (f572c53) into master (b6d8e00) will increase coverage by 11.97%.
The diff coverage is 91.73%.

@@             Coverage Diff             @@
##           master     #161       +/-   ##
===========================================
+ Coverage   84.22%   96.20%   +11.97%     
===========================================
  Files          12       10        -2     
  Lines         748      553      -195     
===========================================
- Hits          630      532       -98     
+ Misses        118       21       -97     

Flag	Coverage Δ
unittests	96.20% <91.73%> (+11.97%)	⬆️

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Impacted Files	Coverage Δ
test/test_models.py	94.87% <89.58%> (-5.13%)	⬇️
test/test_data_pipeline.py	100.00% <100.00%> (ø)
test/test_engine.py	100.00% <100.00%> (ø)
test/test_image_utils.py	100.00% <100.00%> (ø)
test/test_models_anchor_utils.py	100.00% <100.00%> (ø)
test/test_models_common.py	100.00% <100.00%> (ø)
test/test_models_transform.py	100.00% <100.00%> (ø)
test/test_onnx.py	85.24% <100.00%> (-0.47%)	⬇️
test/test_utils.py	88.88% <100.00%> (-11.12%)	⬇️

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