Skip flaky PHP tests in plugin to fix CI failures

[savil]

Problem

The cli-tests on main are failing due to a flaky PHP test in nixpkgs. The php-dom extension has a test (gh10234.phpt) that fails intermittently during the build process.

Error from Oct 24 run:

building '/nix/store/4m46w082habdfswbjagviz3b43g86c8z-php-dom-8.2.29.drv'...
error: builder for '/nix/store/4m46w082habdfswbjagviz3b43g86c8z-php-dom-8.2.29.drv' failed with exit code 2;

FAILED TEST SUMMARY
---------------------------------------------------------------------
GH-10234 (Setting DOMAttr::textContent results in an empty attribute value.) [tests/gh10234.phpt]

Root Cause

This is an upstream nixpkgs issue, not a devbox problem. The PHP DOM extension test is flaky and occasionally fails during the build process. Since we're not modifying PHP itself, these upstream test failures shouldn't block our CI.

Solution

Add doCheck = false and doInstallCheck = false to the PHP package in the plugin flake. This skips all tests during the PHP build, preventing flaky upstream tests from breaking our CI.

Changes

• plugins/php/flake.nix: Override PHP package attributes to skip tests

Context

• The GitHub API rate limiting issue was already fixed in PR Fix GitHub API rate limiting in cli-tests #2731 (merged Oct 23)
• The Oct 23 run succeeded after that fix
• This Oct 24 failure is a separate issue with flaky PHP tests in nixpkgs

Testing

This PR will trigger cli-tests. The examples/plugins/builtin test should now pass without hitting the php-dom test failure.

[savil]

Closing this PR - creating a new one with a cleaner approach (updating PHP version instead of modifying flake)