gha: Add lb4lb test for v1.12 branch
gha: Add lb4lb test for v1.12 branch

Similar to what we have with ci-l4lb-1.11, this is for newly branch-off
1.12.

Suggested-by: Michi Mutsuzaki <a75494f12f73453b2bd75573f87b8f21fcc50565@isovalent.com>
Signed-off-by: Tam Mach <2524536bcff1dac29d2f6b38b02eb7c94efb5019@cilium.io>

cilium/cilium,cilium/cilium,michi-covalent/cilium,cilium/cilium,michi-covalent/cilium,cilium/cilium,michi-covalent/cilium,michi-covalent/cilium,michi-covalent/cilium,cilium/cilium