Add missing void return types to test modules

Problem/Motivation

Splitting up #3550884: Add return types to test module code for smaller scope and easier reviews.

This issue runs the following rector rules on test modules:

• AddFunctionVoidReturnTypeWhereNoReturnRector
• AddTestsVoidReturnTypeWhereNoReturnRector
• AddVoidReturnTypeWhereNoReturnRector

This adds 263 return types across 160 files.

Steps to reproduce

Proposed resolution

Install rector

composer require --dev rector/rector

Configure rector.php file

<?php

use Rector\TypeDeclaration\Rector\Class_\AddTestsVoidReturnTypeWhereNoReturnRector;
use Rector\TypeDeclaration\Rector\ClassMethod\AddVoidReturnTypeWhereNoReturnRector;
use Rector\TypeDeclaration\Rector\Function_\AddFunctionVoidReturnTypeWhereNoReturnRector;

return Rector\Config\RectorConfig::configure()
  ->withPaths([
    __DIR__ . '/core/modules/*/tests/modules',
    __DIR__ . '/core/modules/config/tests/config_*',
    __DIR__ . '/core/modules/dynamic_page_cache/tests/dynamic_page_cache_test',
    __DIR__ . '/core/modules/file/tests/file_*',
    __DIR__ . '/core/modules/filter/tests/filter_*',
    __DIR__ . '/core/modules/language/tests/language_*',
    __DIR__ . '/core/modules/language/tests/test_module',
    __DIR__ . '/core/modules/menu_link_content/tests/menu_*',
    __DIR__ . '/core/modules/menu_link_content/tests/outbound_*',
    __DIR__ . '/core/modules/navigation/tests/navigation_*',
    __DIR__ . '/core/modules/node/tests/node_*',
    __DIR__ . '/core/modules/options/tests/options_*',
    __DIR__ . '/core/modules/serialization/tests/serialization_test',
  ])
  ->withRules([
    AddFunctionVoidReturnTypeWhereNoReturnRector::class,
    AddTestsVoidReturnTypeWhereNoReturnRector::class,
    AddVoidReturnTypeWhereNoReturnRector::class,
  ]);

Run rector
$ ./vendor/bin/rector

Fix code style
$ composer phpcbf

Update baseline
$ ./vendor/bin/phpstan analyse -c core/phpstan.neon.dist --generate-baseline=core/.phpstan-baseline.php --memory-limit=2G

Diff stat

$ git diff --shortstat core/modules
 160 files changed, 263 insertions(+), 263 deletions(-)
$ git diff --shortstat core/.phpstan-baseline.php
 1 file changed, 1578 deletions(-)

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet