Fix panic from wrong type conversion in ng rules

[lewinski]

Description

This fixes a panic caused by a wrong type conversion in the NAT Gateway scanner rules (copy-paste issue) since 2.0.0:

panic: interface conversion: interface {} is *armnetwork.NatGateway, not *armnetwork.SecurityGroup

goroutine 172 [running]:
github.com/Azure/azqr/internal/scanners/ng.(*NatGatewayScanner).GetRecommendations.func4({0xc4df5a0?, 0xc00040a960?}, 0xc000180f90?)

Issue reference

n/a

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Unit tests passing

[cmendible]

wow thanks for this one. I stashed those changes yesterday and never popped them before the release.

[cmendible]

LGTM