Test that docs build on CI

[martin-t]

Currently the docs are broken https://docs.rs/crate/tensorflow/0.17.0

Idk what the issue is but it should be noted that docs.rs uses nightly. You can look at a hopefully properly implemented GH action for example here

[dskkato]

The reason the docs in docs.rs is broken is due to limited network access: see #255. Currently, the doc is posted to github.io

Still, I think it is nice to have doc test in GitHub CI. We already have build-check for the doc via test-all though.

rust/test-all

Lines 55 to 56 in e4f9134

	run cargo doc -vv --features tensorflow_unstable
	run cargo doc -vv --features tensorflow_unstable,private-docs-rs

[dskkato]

I am still not sure why issue #255 is not resolved, even though the private-docs-rs feature was introduced to avoid downloading large files when building docs.