Isolate altcoins tests in their own folder

BTCPayServer/Services/BTCPayServerEnvironment.cs

@@ -72,6 +72,9 @@ namespace BTCPayServer.Services
         {
             StringBuilder txt = new StringBuilder();
             txt.Append($"@Copyright BTCPayServer v{Version}");
+#if ALTCOINS
+            txt.Append($" (altcoins)");
+#endif
             if (!Environment.IsProduction() || !Build.Equals("Release", StringComparison.OrdinalIgnoreCase))
             {
                 txt.Append($" Environment: {Environment.EnvironmentName} Build: {Build}");