Issue #3382624 by adamps: embed attachments adjustment for 2.x

Closes #3382624

src/BaseEmail.php

@@ -257,7 +257,6 @@ class BaseEmail implements BaseEmailInterface {
    * {@inheritdoc}
    */
   public function attachFromPath(string $path, ?string $name = NULL, ?string $mimeType = NULL) {
-    @trigger_error('\Drupal\symfony_mailer\Email::attachFromPath() is deprecated in symfony_mailer:1.6.0 and is removed from symfony_mailer:2.0.0. Use ::attach() instead. See https://www.drupal.org/node/3476132', E_USER_DEPRECATED);
     return $this->attach(Attachment::fromPath($path, $name, $mimeType));
   }
 
@@ -274,13 +273,8 @@ class BaseEmail implements BaseEmailInterface {
    */
   public function attach(AttachmentInterface $attachment): static {
     $this->valid();
-    if ($uri = $attachment->getUri()) {
-      $this->attachments[$uri] = $attachment;
-    }
-    else {
-      $this->attachments[] = $attachment;
-    }
-
+    $key = $attachment->getUri() ?: $attachment->getContentId();
+    $this->attachments[$key] = $attachment;
     return $this;
   }
 
@@ -294,7 +288,7 @@ class BaseEmail implements BaseEmailInterface {
   /**
    * {@inheritdoc}
    */
-  public function removeAttachment($key): static {
+  public function removeAttachment(string $key): static {
     $this->valid();
     unset($this->attachments[$key]);
     return $this;