[LyX/2.4.x] Fixup 39c7199a: the code did not do what it was supposed to

[Jean-Marc Lasgouttes]

commit 312dacb7f32ce5465e1fe3d5d7ac5e0b9b51e045
Author: Jean-Marc Lasgouttes <lasgouttes at lyx.org>
Date:   Wed Jun 5 23:05:22 2024 +0200

    Fixup 39c7199a: the code did not do what it was supposed to
    
    (cherry picked from commit 92ef555abde86466b7ca3c3401ab8132258fc497)
---
 src/insets/InsetLayout.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/insets/InsetLayout.h b/src/insets/InsetLayout.h
index 7593d844d5..ffa0380f17 100644
--- a/src/insets/InsetLayout.h
+++ b/src/insets/InsetLayout.h
@@ -200,7 +200,7 @@ public:
 	///
 	bool docbookrenderasimage() const { return docbookrenderasimage_; }
 	///
-	std::set<std::string> required() const & { return required_; }
+	std::set<std::string> const & required() const { return required_; }
 	///
 	bool isMultiPar() const { return multipar_; }
 	///