payloads/external/GRUB2: fix constantly rebuilding due to git checkout

Multiple git checkouts cause GRUB2 to constantly rebuild even if there
were no changes to code or config. This is due to changing timestamps.

Fix this by not creating or switching branches but instead rely on
`git checkout -f` which does not touch existing unchanged files.

To be sure to not break anyones workflow checkout is skipped and a
warning gets printed if the tree/index is unclean.

Change-Id: I7cf66f63268de973a654146a0a47c3d5ca516d4d
Signed-off-by: Michael Niewöhner <foss@mniewoehner.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36343
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

0 files changed, 0 insertions, 0 deletions