Add 'Missing Override annotation'

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Author: edburns

src/main/java/com/github/copilot/sdk/json/BlobAttachment.java

@@ -45,6 +45,7 @@ public final class BlobAttachment implements MessageAttachment {
      *
      * @return {@code "blob"}
      */
+    @Override
     public String getType() {
         return type;
     }