Fail with error when double-rendering text in markdownify/RenderString

This commit prevents the most commons case of infinite recursion in link render hooks when the `linkify` option is enabled (see below). This is always a user error, but getting a `stack overflow` (the current stack limit in Go is 1 GB on 64-bit, 250 MB on 32-bit) error isn't very helpful. This fix will not prevent all such errors, though, but we may do better once #9570 is in place.

So, these will fail:

```
<a href="{{ .Destination | safeURL }}" >{{ .Text | markdownify }}</a>
<a href="{{ .Destination | safeURL }}" >{{ .Text | .Page.RenderString }}</a>
```

`.Text` is already rendered to `HTML`. The above needs to be rewritten to:

```
<a href="{{ .Destination | safeURL }}" >{{ .Text | safeHTML }}</a>
<a href="{{ .Destination | safeURL }}" >{{ .Text | safeHTML }}</a>
```

Fixes #8959

markup/goldmark/integration_test.go

@@ -18,6 +18,8 @@ import (
 	"strings"
 	"testing"
 
+	qt "github.com/frankban/quicktest"
+
 	"github.com/gohugoio/hugo/hugolib"
 )
 
@@ -395,6 +397,49 @@ FENCE
 	}
 }
 
+// Iisse #8959
+func TestHookInfiniteRecursion(t *testing.T) {
+	t.Parallel()
+
+	for _, renderFunc := range []string{"markdownify", ".Page.RenderString"} {
+		t.Run(renderFunc, func(t *testing.T) {
+
+			files := `
+-- config.toml --
+-- layouts/_default/_markup/render-link.html --
+<a href="{{ .Destination | safeURL }}">{{ .Text | RENDERFUNC }}</a>	
+-- layouts/_default/single.html --
+{{ .Content }}
+-- content/p1.md --
+---
+title: "p1"
+---
+
+https://example.org
+
+a@b.com
+		
+			
+			`
+
+			files = strings.ReplaceAll(files, "RENDERFUNC", renderFunc)
+
+			b, err := hugolib.NewIntegrationTestBuilder(
+				hugolib.IntegrationTestConfig{
+					T:           t,
+					TxtarString: files,
+				},
+			).BuildE()
+
+			b.Assert(err, qt.IsNotNil)
+			b.Assert(err.Error(), qt.Contains, "text is already rendered, repeating it may cause infinite recursion")
+
+		})
+
+	}
+
+}
+
 // Issue 9594
 func TestQuotesInImgAltAttr(t *testing.T) {
 	t.Parallel()