Revert "[ci] remove IS_GHA env var"
This reverts commit 1a2d95c68a11dd95b4699e7a74d679d8b9a5fb5a.
Reverted https://github.com/pytorch/pytorch/pull/79219 on behalf of https://github.com/malfet due to Broke binary jobs see https://hud.pytorch.org/pytorch/pytorch/commit/1a2d95c68a11dd95b4699e7a74d679d8b9a5fb5a
