Fix pattern name, and use pattern in template part (#7206)

fotograma/parts/header.html

@@ -1,5 +1 @@
-<!-- wp:group {"style":{"spacing":{"blockGap":"0px"}},"layout":{"type":"default"}} -->
-<div class="wp-block-group">
-	<!-- wp:site-title {"style":{"spacing":{"margin":{"top":"0px","bottom":"0px","right":"0px","left":"0px"}}}} /-->
-</div>
-<!-- /wp:group -->
+<!-- wp:pattern {"slug":"fotograma/header"} /-->

fotograma/patterns/header.php

@@ -1,8 +1,8 @@
 <?php
 /**
- * Title: Stack Photo
+ * Title: Header
  * Slug: fotograma/header
- * Categories: featured
+ * Categories: featured, header
  */
 ?>