Update zone-sync headless service selector label

[pdabelf5]

Proposed changes

Fix selector labels for zonesync headless service

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 52.77%. Comparing base (9a0a3f7) to head (f2e526a).
Report is 11 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/nginx-ingress/main.go	0.00%	1 Missing ⚠️
internal/k8s/service.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7445   +/-   ##
=======================================
  Coverage   52.76%   52.77%           
=======================================
  Files          89       89           
  Lines       21267    21267           
=======================================
+ Hits        11221    11223    +2     
+ Misses       9582     9580    -2     
  Partials      464      464           

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