[8.x] Clarifies parallel testing token type (#39403)

* Fixes token type

* Improves test

Author: nunomaduro

src/Illuminate/Testing/ParallelTesting.php

@@ -257,7 +257,7 @@ public function option($option)
     /**
      * Gets a unique test token.
      *
-     * @return int|false
+     * @return string|false
      */
     public function token()
     {

tests/Testing/ParallelTestingTest.php

@@ -36,15 +36,15 @@ public function testCallbacks($callback)
                 $this->assertNull($testCase);
             }
 
-            $this->assertEquals(1, $token);
+            $this->assertSame('1', $token);
             $state = true;
         });
 
         $parallelTesting->{$caller}($this);
         $this->assertFalse($state);
 
         $parallelTesting->resolveTokenUsing(function () {
-            return 1;
+            return '1';
         });
 
         $parallelTesting->{$caller}($this);
@@ -80,10 +80,10 @@ public function testToken()
         $this->assertFalse($parallelTesting->token());
 
         $parallelTesting->resolveTokenUsing(function () {
-            return 1;
+            return '1';
         });
 
-        $this->assertSame(1, $parallelTesting->token());
+        $this->assertSame('1', $parallelTesting->token());
     }
 
     public function callbacks()