Fix path resolution in hugo new

With theme and project with content directories and command on the form `hugo new posts/test.md`.

Fixes #9129

create/content_test.go

@@ -35,7 +35,7 @@ import (
 )
 
 // TODO(bep) clean this up. Export the test site builder in Hugolib or something.
-func TestNewContent(t *testing.T) {
+func TestNewContentFromFile(t *testing.T) {
 	cases := []struct {
 		name     string
 		kind     string