🐛: elbv2: skip adding security groups to NLB in secret regions

[r4f4]

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Secret regions don't yet support security groups for NLBs.

What type of PR is this?

/kind bug

What this PR does / why we need it:

C2S/SC2S regions do not support security groups on Network load balancers.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged): Fixes #5029

Special notes for your reviewer:

Checklist:

• [X] squashed commits
• [ ] includes documentation
• [X] includes emojis
• [ ] adds unit tests
• [ ] adds or updates e2e tests

Release note:

Fix: do not attach security groups for Network Load Balancers in secret regions.