fix(tests): replace UsesClass with CoversClass for DiscoveryException

PHPUnit 12 with beStrictAboutCoverageMetadata emits a warning when
#[UsesClass] targets a class that cannot be instrumented.
DiscoveryException extends \RuntimeException (a PHP built-in), which
PCOV cannot fully instrument via UsesClass semantics.

- DiscoveryExceptionTest: UsesClass → CoversClass (the test directly
  exercises DiscoveryException, so CoversClass is correct).
- DirectoryScannerTest:  UsesClass(DiscoveryException) → CoversClass
  (testScanNonExistentPathThrowsException exercises the exception path).

Eliminates all 26 PHPUnit Warnings that were failing the CI pipeline.

Author: walmir-silva

tests/Unit/Exception/DiscoveryExceptionTest.php

@@ -5,10 +5,10 @@
 namespace KaririCode\ClassDiscovery\Tests\Unit\Exception;
 
 use KaririCode\ClassDiscovery\Exception\DiscoveryException;
-use PHPUnit\Framework\Attributes\UsesClass;
+use PHPUnit\Framework\Attributes\CoversClass;
 use PHPUnit\Framework\TestCase;
 
-#[UsesClass(DiscoveryException::class)]
+#[CoversClass(DiscoveryException::class)]
 final class DiscoveryExceptionTest extends TestCase
 {
     #[\PHPUnit\Framework\Attributes\DataProvider('namedConstructorProvider')]

tests/Unit/Scanner/DirectoryScannerTest.php

@@ -19,10 +19,10 @@
 use PHPUnit\Framework\TestCase;
 
 #[CoversClass(DirectoryScanner::class)]
+#[CoversClass(DiscoveryException::class)]
 #[UsesClass(FileScanner::class)]
 #[UsesClass(ConcreteDiscoveryResult::class)]
 #[UsesClass(ClassMetadata::class)]
-#[UsesClass(DiscoveryException::class)]
 
 final class DirectoryScannerTest extends TestCase
 {