CppEditor: Verify proper highlighting of the concept keyword

Change-Id: I1c814da472f10539f87640a52822b188b9b7a2cd
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/cppeditor/cpphighlighter.cpp

@@ -513,6 +513,7 @@ void CppHighlighterTest::test_data()
     QTest::newRow("struct keyword") << 25 << 1 << 25 << 6 << C_KEYWORD;
     QTest::newRow("operator keyword") << 26 << 5 << 26 << 12 << C_KEYWORD;
     QTest::newRow("type in conversion operator") << 26 << 14 << 26 << 16 << C_PRIMITIVE_TYPE;
+    QTest::newRow("concept keyword") << 29 << 22 << 29 << 28 << C_KEYWORD;
 }
 
 void CppHighlighterTest::test()

src/plugins/cppeditor/testcases/highlightingtestcase.cpp

@@ -25,3 +25,5 @@ template<int n = 5> class C;
 struct ConversionFunction {
     operator int();
 };
+
+template<typename T> concept NoConstraint = true;