Mark websubhub:PublisherClient as an isolated client

[ayeshLK]

Purpose

$subject

Fixes: ballerina-platform/ballerina-library#8498

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.16%. Comparing base (4e951f1) to head (2d28b64).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1114      +/-   ##
============================================
+ Coverage     89.14%   89.16%   +0.01%     
  Complexity       47       47              
============================================
  Files            16       16              
  Lines           857      858       +1     
  Branches        234      234              
============================================
+ Hits            764      765       +1     
  Misses           89       89              
  Partials          4        4              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.