FIX Pass variant args into array_merge correctly

Without this, trying to pass any variant name into variantParts() will
result in `TypeError: array_merge(): Argument #2 must be of type array,
string given`

This wasn't caught until now because `variantParts()` isn't actually
used anywhere in our codebase.

src/ImageManipulation.php

@@ -1037,7 +1037,7 @@ public function variantParts($variantName)
             throw new InvalidArgumentException('Invalid variant name arguments: ' . $variantName);
         }
 
-        return array_merge([$matches['format']], $args[0]);
+        return array_merge([$matches['format']], $args);
     }
 
     /**

tests/php/ImageTest.php

@@ -419,7 +419,7 @@ public function testVariantParts()
         $image = singleton(Image::class);
         $format = 'Pad';
         $args = [331, 313, '222222', 0];
-        $name = $image->variantName($format, $args);
+        $name = $image->variantName($format, ...$args);
         $this->assertEquals(
             array_merge([$format], $args),
             $image->variantParts($name)
@@ -432,7 +432,7 @@ public function testVariantPartsThrowsOnInvalidName()
         /** @var Image $image */
         $image = singleton(Image::class);
         $args = ['foo'];
-        $name = $image->variantName('Invalid', $args);
+        $name = $image->variantName('Invalid', ...$args);
         $image->variantParts($name);
     }