Replaced to_tensor() with pil_to_tensor() + convert_image_dtype()

[zhiqwang]

Follow the upstream pytorch/vision#4452 .

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[codecov]

Codecov Report

Merging #298 (63b9756) into main (61df774) will not change coverage.
The diff coverage is n/a.

❗ Current head 63b9756 differs from pull request most recent head 0000ad1. Consider uploading reports for the commit 0000ad1 to get more accurate results

@@           Coverage Diff           @@
##             main     #298   +/-   ##
=======================================
  Coverage   94.01%   94.01%           
=======================================
  Files          11       11           
  Lines         718      718           
=======================================
  Hits          675      675           
  Misses         43       43           

Flag	Coverage Δ
unittests	94.01% <ø> (ø)

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