Configure php_unit_data_provider_return_type fixer

[paulbalandan]

Description

$ vendor/bin/php-cs-fixer describe php_unit_data_provider_return_type
Description of php_unit_data_provider_return_type rule.
The return type of PHPUnit data provider must be `iterable`.
Data provider must return `iterable`, either an array of arrays or an object that implements the `Traversable` interface.

Fixer applying this rule is risky.
Risky when relying on signature of the data provider.

Fixing examples:
 * Example #1.
   ---------- begin diff ----------
   --- Original
   +++ New
   @@ -1,8 +1,8 @@
    <?php
    class FooTest extends TestCase {
        /**
         * @dataProvider provideSomethingCases
         */
        public function testSomething($expected, $actual) {}
   -    public function provideSomethingCases(): array {}
   +    public function provideSomethingCases(): iterable {}
    }

   ----------- end diff -----------

 * Example #2.
   ---------- begin diff ----------
   --- Original
   +++ New
   @@ -1,8 +1,8 @@
    <?php
    class FooTest extends TestCase {
        /**
         * @dataProvider provideSomethingCases
         */
        public function testSomething($expected, $actual) {}
   -    public function provideSomethingCases() {}
   +    public function provideSomethingCases(): iterable {}
    }

   ----------- end diff -----------

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[kenjis]

"Coding Standards / PHP 7.4 Lint with PHP CS Fixer (pull_request)" fails.