typings(Attachment): make attachment private (#8982)

* typings(Attachment): remove attachment property

* remove from structures

* Revert "remove from structures"

This reverts commit 88acb8d.

* typings(attachment): make attachment private

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Co-authored-by: space <spaceeec@yahoo.com>
Co-authored-by: kodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>

packages/discord.js/typings/index.d.ts

@@ -1988,7 +1988,7 @@ export class AttachmentBuilder {
 
 export class Attachment {
   private constructor(data: APIAttachment);
-  public attachment: BufferResolvable | Stream;
+  private attachment: BufferResolvable | Stream;
   public contentType: string | null;
   public description: string | null;
   public ephemeral: boolean;