markup/goldmark: Fix data race in the hugocontext wrapper

The window for this to happen is very small, but it has been reported by Go's race detector (-race flag) in a tests once.

hugolib/page__per_output.go

@@ -175,7 +175,7 @@ func (pco *pageContentOutput) RenderShortcodes(ctx context.Context) (template.HT
 		// This content will be parsed and rendered by Goldmark.
 		// Wrap it in a special Hugo markup to assign the correct Page from
 		// the stack.
-		c = hugocontext.Wrap(c, pco.po.p.pid)
+		return template.HTML(hugocontext.Wrap(c, pco.po.p.pid)), nil
 	}
 
 	return helpers.BytesToHTML(c), nil

markup/goldmark/hugocontext/hugocontext.go

@@ -34,7 +34,7 @@ func New() goldmark.Extender {
 
 // Wrap wraps the given byte slice in a Hugo context that used to determine the correct Page
 // in .RenderShortcodes.
-func Wrap(b []byte, pid uint64) []byte {
+func Wrap(b []byte, pid uint64) string {
 	buf := bufferpool.GetBuffer()
 	defer bufferpool.PutBuffer(buf)
 	buf.Write(prefix)
@@ -45,7 +45,7 @@ func Wrap(b []byte, pid uint64) []byte {
 	buf.Write(b)
 	buf.Write(prefix)
 	buf.Write(closingDelimAndNewline)
-	return buf.Bytes()
+	return buf.String()
 }
 
 var kindHugoContext = ast.NewNodeKind("HugoContext")

markup/goldmark/hugocontext/hugocontext_test.go

@@ -24,7 +24,7 @@ func TestWrap(t *testing.T) {
 
 	b := []byte("test")
 
-	c.Assert(string(Wrap(b, 42)), qt.Equals, "{{__hugo_ctx pid=42}}\ntest{{__hugo_ctx/}}\n")
+	c.Assert(Wrap(b, 42), qt.Equals, "{{__hugo_ctx pid=42}}\ntest{{__hugo_ctx/}}\n")
 }
 
 func BenchmarkWrap(b *testing.B) {