(maint) Force english culture on exception test

This commit updates a test that verifies that a test that reports
an exception is running under the English culture.
This is done so the test won't fail when it is running on
non-english cultures just because the messaging would be
different.

src/chocolatey.tests.integration/infrastructure.app/services/FilesServiceSpecs.cs

@@ -46,6 +46,7 @@ public override void Context()
             }
         }
 
+        [SetCulture("en"), SetUICulture("en")]
         public class when_FilesService_encounters_locked_files : FilesServiceSpecsBase
         {
             private PackageFiles _result;