Backport of #26742 to release/1.17.
RunsOn v2.12.0 (March 6, 2026) removed v1 cache toolkit support,
causing the buildx GHA cache proxy to return 404 for v1 endpoints.
This broke the v1.17.0-rc2 container build.
Removing the explicit version=1 parameter lets buildkit auto-detect
the v2 protocol.
Signed-off-by: Ramon Roche <mrpollo@gmail.com>