[CI] replace header validation test with frgfm 's action

[felixdittrich92]

This PR:

• replaces header validation test with @frgfm 's action (https://github.com/frgfm/validate-python-headers thanks for this ❤️ )

related to: #957

[codecov]

Codecov Report

Merging #1030 (d646053) into main (faf5590) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1030   +/-   ##
=======================================
  Coverage   94.93%   94.93%           
=======================================
  Files         135      135           
  Lines        5590     5590           
=======================================
  Hits         5307     5307           
  Misses        283      283           

Flag	Coverage Δ
unittests	94.93% <ø> (ø)

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

Impacted Files	Coverage Δ
doctr/datasets/cord.py	97.72% <ø> (ø)
doctr/datasets/datasets/base.py	98.00% <ø> (ø)
doctr/datasets/datasets/pytorch.py	100.00% <ø> (ø)
doctr/datasets/datasets/tensorflow.py	100.00% <ø> (ø)
doctr/datasets/detection.py	95.65% <ø> (ø)
doctr/datasets/doc_artefacts.py	93.93% <ø> (ø)
doctr/datasets/funsd.py	97.43% <ø> (ø)
doctr/datasets/generator/base.py	81.08% <ø> (ø)
doctr/datasets/generator/pytorch.py	100.00% <ø> (ø)
doctr/datasets/generator/tensorflow.py	100.00% <ø> (ø)
... and 90 more

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[odulcy-mindee]

Thanks @felixdittrich92 and @frgfm ! LGTM

[felixdittrich92]

Thanks @felixdittrich92 and @frgfm ! LGTM

Thanks goes to @frgfm 🤗

[frgfm]

Haha, glad it helped :)