Move go generate diff check into a separate job.

[VitalyGushin]

https://github.com/networkservicemesh/govpp/issues/30

[glazychev-art]

@VitalyGushin Check generated files failed, but it should be green. Do you have any idea?

I guess it is related to the diff, which actually looks like this: https://github.com/networkservicemesh/govpp/actions/runs/8252757728/job/22573172614#step:7:15

-//  VPP:              23.10-rc0~170-g6f1548434
+//  VPP:              23.10-rc0~170-gfb4b9fae3

Can we skip these lines somehow?

[VitalyGushin]

@glazychev-art The new job failed because it works ("go generate" produces diff). I may run "go generate" locally and add these changes to the PR to make the job green.