Repair wp/6.0 branch Actions: Use PHPUnit Polyfills' fixture method names - #84280

Part of #82933.

What?

Fixes a fatal error, identical across all six PHP 7.4/8.0/8.1 (single-site and multisite) unit-test.yml legs, that blocks PHPUnit from even starting the test suite.

Why?

#84279 (the base of this PR) bumped wp-phpunit/wp-phpunit to 6.0.x, which makes WP_UnitTestCase extend yoast/phpunit-polyfills' TestCase. That class declares setUp(), tearDown(), setUpBeforeClass() and tearDownAfterClass() with a : void return type. Subclasses are expected to override the snake_case set_up(), tear_down(), set_up_before_class() and tear_down_after_class() methods instead, which work on PHP versions without void return types.

Nine test classes in this repository still override the camelCase methods without a return type. On PHP 7.1 and later, that is an incompatible declaration:

Fatal error: Declaration of WP_Block_Supports_Layout_Test::setUp() must be compatible with
Yoast\PHPUnitPolyfills\TestCases\TestCase::setUp(): void in phpunit/block-supports/layout-test.php

This affects the PHP 7.4, 8.0 and 8.1 jobs in the current matrix.

How?

Renames each affected method to its Polyfills name, including the corresponding parent:: call where one exists. Differences between files:

• phpunit/class-wp-webfonts-local-provider-test.php already had a correctly-named tear_down(); only its setUp() needed renaming.
• phpunit/navigation-test.php's setUp()/tearDown() never call parent::setUp()/parent::tearDown(), so only the method names themselves needed changing.
• phpunit/navigation-page-test.php is the only file with static setUpBeforeClass()/tearDownAfterClass() overrides in addition to the instance methods — all four needed renaming.
• phpunit/class-wp-test-rest-users-controller.php also defines wpSetUpBeforeClass()/wpTearDownAfterClass() — a separate, WP-specific factory convention (not PHPUnit's own fixture methods) — left untouched.

Use of AI Tools

This PR was created by Claude Code under my supervision. All code should be treated as AI-produced and not yet reviewed by a human until this PR is marked Ready for Review.