Fix error when updating health check settings in TGC for Gateway API ALB target groups

[shraddhabang]

Issue

#4740

Description

Two bugs in isSDKTargetGroupRequiresReplacementDueToNLBHealthCheck:

1. isL4TargetGroup switch had empty case bodies that did not fall through (Go semantics), so only TCP_UDP returned true
2. Guard logic was inverted — skipped replacement for NLB and forced replacement for ALB

Checklist

• Added tests that cover your change (if possible)
• Added/modified documentation as required (such as the README.md, or the docs directory)
• Manually tested
• Made sure the title of the PR is a good description that can go into the release notes

BONUS POINTS checklist: complete for good vibes and maybe prizes?! 🤯

• Backfilled missing tests for code in same general area 🎉
• Refactored something and made the world a better place 🌟

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 56.24%. Comparing base (22cdb42) to head (5f7d397).
⚠️ Report is 24 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4741      +/-   ##
==========================================
+ Coverage   56.09%   56.24%   +0.14%     
==========================================
  Files         388      390       +2     
  Lines       30932    31040     +108     
==========================================
+ Hits        17352    17459     +107     
- Misses      12566    12570       +4     
+ Partials     1014     1011       -3     

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[zac-nixon]

/lgtm
/approved

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: shraddhabang, zac-nixon

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Details

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• OWNERS [shraddhabang,zac-nixon]

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[shuqz]

/approved