Fix doc version (#3310)

Summary:
Fixes the regression caused by build_doc job GHA migration. The version number is not properly set.

Pull Request resolved: https://github.com/pytorch/audio/pull/3310

Reviewed By: nateanl

Differential Revision: D45607829

Pulled By: mthrok

fbshipit-source-id: 3450a38fa6982fcc56676a80144e9eed1aad02ec

.github/workflows/build_docs.yml

@@ -63,6 +63,10 @@ jobs:
         # TODO: Enable NVDec/NVEnc
         conda install --quiet -y 'ffmpeg>=4.1' pkg-config
         pip --quiet install cmake>=3.18.0 ninja
+        cd packaging
+        . ./pkg_helpers.bash
+        setup_build_version
+        cd ../
         USE_FFMPEG=1 pip install --progress-bar off -v -e . --no-use-pep517
 
         # Install runtime dependencies