Skip empty filenames in configuration loading

Update GetConfigurationRoot to ignore TestAppSettings entries with null or empty filenames when adding JSON files to the configuration builder.

Author: Arash-Sabet

src/Abstracts/TestBedFixture.cs

@@ -155,7 +155,7 @@ private IConfigurationRoot GetConfigurationRoot()
 
 	private IConfigurationRoot GetConfigurationRoot(IEnumerable<TestAppSettings> configurationFiles)
 	{
-		foreach (var configurationFile in configurationFiles)
+		foreach (var configurationFile in configurationFiles.Where(appSetting => !string.IsNullOrEmpty(appSetting.Filename)))
 		{
 			ConfigurationBuilder.AddJsonFile(configurationFile.Filename!, optional: configurationFile.IsOptional);
 		}