config/module: fix panic on Windows when running tests

On Windows, Go returns paths with the `\` path separator.
Make sure we are using `/` even on Windows since URLs are `/`-based.

config/module/module_test.go

@@ -42,7 +42,7 @@ func testModule(n string) string {
 
 	var url url.URL
 	url.Scheme = "file"
-	url.Path = p
+	url.Path = filepath.ToSlash(p)
 	return url.String()
 }