Fix for breadcrumbs displaying "Old version (stable)" on Nightly build

[carljparker]

Previously, breadcrumbs.html identified a nightly build version by the prefix "Nightly" which would normally be prepended to the version in conf.py. However, the version string is coming through without the "Nightly" prefix, so this change causes breadcrumbs.html to key on the substring "dev" instead.

The reason we aren't getting "Nightly" is apparently because the environment variable BUILD_VERSION is available, so conf.py is using the value of that env var instead of the version string imported from the torchaudio module itself, which actually appears to be incorrect; see below.

If I install torchaudio using

conda install torchaudio -c pytorch-nightly

then torchaudio.__version__ returns the incorrect version string:

2.0.0.dev20230309

[pytorch-bot]

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As of commit 78429e7:

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• build (3.8) (gh)

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[mthrok]

Looks good. Thanks!

[facebook-github-bot]

@carljparker has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

[facebook-github-bot]

@carljparker merged this pull request in 3ffd76c.

[github-actions]

Hey @carljparker.
You merged this PR, but labels were not properly added. Please add a primary and secondary label (See https://github.com/pytorch/audio/blob/main/.github/process_commit.py).

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Some guidance:

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