[LyX/2.3.x] Avoid some more copies in range-based for loops

[Jean-Marc Lasgouttes]

commit cca4b8d42a282d3b93d86acb0e990074db4f7fd3
Author: Jean-Marc Lasgouttes <lasgouttes at lyx.org>
Date:   Fri Oct 15 16:10:04 2021 +0200

    Avoid some more copies in range-based for loops
    
    This triggers warnings with clang++ 10 and gcc 11.
    
    (cherry-picked from commit 7035e230caa69a2e35f16dcf0d9696c59cef5c4c)
---
 src/frontends/qt4/Menus.cpp |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/frontends/qt4/Menus.cpp b/src/frontends/qt4/Menus.cpp
index 5f9eb90..a2505dc 100644
--- a/src/frontends/qt4/Menus.cpp
+++ b/src/frontends/qt4/Menus.cpp
@@ -1337,7 +1337,7 @@ void MenuDefinition::expandToc(Buffer const * buf)
 	// In the navigation menu, only add tocs from this document
 	TocBackend const & backend = buf->tocBackend();
 	TocList const & toc_list = backend.tocs();
-	for (pair<string, shared_ptr<Toc>> const & toc : toc_list) {
+	for (pair<const string, shared_ptr<Toc>> const & toc : toc_list) {
 		// Handle table of contents later
 		if (toc.first == "tableofcontents" || toc.second->empty())
 			continue;
@@ -1695,7 +1695,7 @@ void MenuDefinition::expandCaptions(Buffer const * buf, bool switchcap)
 
 	DocumentClass const & dc = buf->params().documentClass();
 	vector< pair<docstring, FuncRequest> > caps;
-	for (pair<docstring, InsetLayout> const & il : dc.insetLayouts()) {
+	for (pair<const docstring, InsetLayout> const & il : dc.insetLayouts()) {
 		docstring instype;
 		docstring const type = split(il.first, instype, ':');
 		if (instype == from_ascii("Caption")) {