[LyX/master] Use C++11 string literals to make code easier to read.

[Thibaut Cuvelier]

commit 6b1441036f35767c0b60af510222ba792b17b829
Author: Thibaut Cuvelier <tcuvelier at lyx.org>
Date:   Mon Feb 26 15:24:36 2024 +0100

    Use C++11 string literals to make code easier to read.
---
 src/insets/InsetIndex.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/insets/InsetIndex.cpp b/src/insets/InsetIndex.cpp
index 68669b0b7e..64bb398099 100644
--- a/src/insets/InsetIndex.cpp
+++ b/src/insets/InsetIndex.cpp
@@ -505,9 +505,9 @@ void InsetIndex::docbook(XMLStream & xs, OutputParams const & runparams) const
 			// Generate the attributes.
 			docstring id = xml::cleanID(newIndexTerms);
 			if (hasStartRange) {
-				attrs = indexType + " class=\"startofrange\" xml:id=\"" + id + "\"";
+				attrs = indexType + R"( class="startofrange" xml:id=")" + id + "\"";
 			} else {
-				attrs = " class=\"endofrange\" startref=\"" + id + "\"";
+				attrs = R"( class="endofrange" startref=")" + id + "\"";
 			}
 		}