update GHES warning behavior

src/internal/shared/errors.ts

@@ -26,3 +26,12 @@ export class ArtifactNotFoundError extends Error {
     this.name = 'ArtifactNotFoundError'
   }
 }
+
+export class GHESNotSupportError extends Error {
+  constructor(
+    message = '@actions/artifact v2.0.0+ and download-artifact@v4+ are not currently supported on GHES.'
+  ) {
+    super(message)
+    this.name = 'NotSupportedGHESError'
+  }
+}

src/internal/shared/interfaces.ts

@@ -56,7 +56,7 @@ export interface GetArtifactResponse {
   /**
    * Metadata about the artifact that was found
    */
-  artifact?: Artifact
+  artifact: Artifact
 }
 
 /*****************************************************************************