Update index.md (#1658)

Specifying type:'datetime' for $publicationDate causes a denormalization failure. Removing it or replacing it with 'datetime_immutable' fixes the issue.

Author: mano-lis

distribution/index.md

@@ -393,7 +393,7 @@ Modify these files as described in these patches:
      public string $author = '';
 
      /** The publication date of this book. */
-+    #[ORM\Column(type: 'datetime')]
++    #[ORM\Column]
      public ?\DateTimeImmutable $publicationDate = null;
 
      /** @var Review[] Available reviews for this book. */
@@ -433,7 +433,7 @@ Modify these files as described in these patches:
      public string $author = '';
 
      /** The date of publication of this review.*/
-+    #[ORM\Column(type: 'datetime')]
++    #[ORM\Column]
      public ?\DateTimeImmutable $publicationDate = null;
 
      /** The book this review is about. */