docs: fix formatting for embedding_bag (#54666)
Summary:
fixes https://github.com/pytorch/pytorch/issues/43499
Pull Request resolved: https://github.com/pytorch/pytorch/pull/54666
Reviewed By: H-Huang
Differential Revision: D27411027
Pulled By: jbschlosser
fbshipit-source-id: a84cc174155bd725e108d8f953a21bb8de8d9d23
