Use the correct lock constant when stream wrapper locks the file

$operation contains `0` value which results to `ValueError: flock(): Argument #2 ($operation) must be one of LOCK_SH, LOCK_EX, or LOCK_UN`

So we explicitly use `LOCK_SH`

Author: maks-rafalko

src/IncludeInterceptor.php

@@ -249,7 +249,7 @@ public function stream_lock($operation)
     {
         assert(is_resource($this->fp));
 
-        return flock($this->fp, $operation);
+        return flock($this->fp, LOCK_SH);
     }
 
     public function stream_metadata($path, $option, $value)

tests/IncludeInterceptorTest.php

@@ -36,12 +36,16 @@
 namespace Infection\Tests\StreamWrapper;
 
 use function count;
+use function file_put_contents;
 use Infection\StreamWrapper\IncludeInterceptor;
 use InvalidArgumentException;
+use function is_link;
 use const PHP_SAPI;
 use PHPUnit\Framework\Error\Warning;
 use PHPUnit\Framework\TestCase;
 use RuntimeException;
+use function symlink;
+use function sys_get_temp_dir;
 
 /**
  * Tests IncludeInterceptor for correct operation.
@@ -433,4 +437,15 @@ public function test_it_respects_symlinks_in_url_stat(): void
 
         $this->assertTrue(is_link($symlink));
     }
+
+    public function test_it_works_with_locks(): void
+    {
+        IncludeInterceptor::intercept(self::$files[1], self::$files[2]);
+        IncludeInterceptor::enable();
+
+        // action - lock the file to check locking does not throw an exception with our stream wrapper
+        file_put_contents(self::$files[1], 'text', LOCK_EX);
+
+        $this->addToAssertionCount(1);
+    }
 }