Since PHP 8.1, calling the `Reflection*::setAccessible()` methods is no longer necessary as reflected properties/methods/etc will always be accessible.
However, the method calls are still needed for PHP < 8.1.
As of PHP 8.5, calling the `Reflection*::setAccessible()` methods is now formally deprecated and will yield a deprecation notice, which will fail test runs.
As of PHP 9.0, the `setAccessible()` method(s) will be removed.
With the latter in mind, this commit prevents the deprecation notice by making the calls to `setAccessible()` conditional.
Silencing the deprecation would mean, this would need to be "fixed" again come PHP 9.0, while the current solution should be stable, including for PHP 9.0.
Ref: https://wiki.php.net/rfc/deprecations_php_8_5#extreflection_deprecations
PHPCS 3.6.2 added a sniff for a PSR-12 rule which was previously not strictly checked: "No blank line after the opening brace of a class".
This fixes the newly flagged issues.
* Tests/reorganize: move OAuth test to own file
This test uses the `Yoast\PHPUnitPolyfills\TestCases\TestCase` instead of the `PHPMailer\Test\TestCase` base class as it doesn't need the `set_up()` or `tear_down()` methods from the PHPMailer base test class.
* OAuthTest: various test tweaks
Minor test tweaks:
* Add `@covers` tags.
* Add "failure" messages to assertions.
* Minor comment punctuation.
Co-authored-by: jrfnl <jrfnl@users.noreply.github.com>