CI: add WP 6.9 and 7.0 to unit test matrix

[rebeccahum]

Description

WordPress latest is now 7.1, so 6.9 and 7.0 dropped out of CI coverage. This pins 6.9.x and 7.0.x in the unit test matrix (single site + multisite, Jetpack on) for PHP 8.2, 8.3 and 8.4, matching the existing per-minor rows.

PHP 8.5 rows are unchanged (still latest only).

Pre-review checklist

• This change works and has been tested locally or in Codespaces (or has an appropriate fallback).
• This change works and has been tested on a sandbox.
• This change has relevant unit tests (if applicable).
• This change uses a rollout method to ease with deployment (if applicable - especially for large scale actions that require writes).
• This change has relevant documentation additions / updates (if applicable).
• I've created a changelog description that aligns with the provided examples.

Steps to Test

1. Check the CI workflow run on this PR.
2. Verify the new WP 6.9.x and WP 7.0.x jobs run for PHP 8.2, 8.3 and 8.4 and pass.

🤖 Generated with Claude Code

[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

[Copilot]

🟢 Approval recommended

The matrix additions are valid, consistent with existing rows, and match the stated scope.

0 open findings

What changed in this PR

Adds explicit WordPress 6.9 and 7.0 CI coverage after latest advanced to 7.1.

Changes:

• Adds single-site and multisite jobs for PHP 8.2–8.4.
• Keeps Jetpack enabled and PHP 8.5 coverage unchanged.

File	Description
.github/​workflows/​ci.yml	Expands the unit-test matrix for WordPress 6.9 and 7.0.

🧠 Review effort: Balanced

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 40.29%. Comparing base (d7026ce) to head (35a90f7).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff             @@
##             develop    #7389   +/-   ##
==========================================
  Coverage      40.29%   40.29%           
  Complexity      5591     5591           
==========================================
  Files            305      305           
  Lines          22192    22192           
==========================================
  Hits            8942     8942           
  Misses         13250    13250           

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