Fix Audiobookshelf PDF upload test setup

Create temporary AccountsSettings.json required by cover-art filename
generation, fixing the missing-file failure in CI.

Refs #2044

Source/_Tests/FileLiberator.Tests/UploadToAudiobookshelfTests.cs

@@ -304,6 +304,8 @@ public class UploadToAudiobookshelfTests
 		{
 			var config = ConfiguredForAudiobookshelf();
 			config.Books = directory;
+			// Cover-art naming reads account nicknames, even when no cover exists.
+			AudibleUtilities.AudibleApiStorage.EnsureAccountsSettingsFileExists();
 			var book = LibraryBookWith(LiberatedStatus.Liberated);
 			var audio = Path.Combine(directory, "B0TEST0001.m4b");
 			var pdf = Path.Combine(directory, "supplement.pdf");