fix listener metadata for MergeGateways

[zirain]

fixes: #6716

[codecov]

Codecov Report

❌ Patch coverage is 97.61905% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 71.03%. Comparing base (14a02b0) to head (cf150e8).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/gatewayapi/runner/runner.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6722      +/-   ##
==========================================
+ Coverage   71.00%   71.03%   +0.02%     
==========================================
  Files         224      224              
  Lines       39606    39618      +12     
==========================================
+ Hits        28122    28141      +19     
+ Misses       9824     9818       -6     
+ Partials     1660     1659       -1     

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[arkodg]

this will cause the same issue as before, because merging listeners, will end up creating new resource metadata since you are adding a section name

[zirain]

internal/gatewayapi/testdata/merge-valid-multiple-gateways2.in.yaml show a stable xds when they use same section.

[zirain]

#6639 reverted, closed.