[small BE] .github: refactor concurrency into a common macro (#64587)
Summary:
By using a macro for these concurrency groups, we can edit just one place for the linux and windows workflows (vs 2).
I wanted to loop all the other workflow files in as well, but since those aren't generated, the macros won't work the same way.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/64587
Reviewed By: mrshenli
Differential Revision: D30783224
Pulled By: janeyx99
fbshipit-source-id: ae16ebb12d2d63a563d28f0ce88e280f68ed4b9b
