qbs build: Use exportingProduct in Export items

The use of product in Export items is deprecated and will be removed in
one of the next qbs versions.

Change-Id: I2644a69012db4a4b4842066784913f4160d3d80a
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/libs/3rdparty/syntax-highlighting/syntax-highlighting.qbs

@@ -55,8 +55,8 @@ Project {
         Export {
             Depends { name: "cpp" }
             cpp.includePaths: [
-                product.sourceDirectory + "/src/lib/",
-                product.sourceDirectory + "/autogenerated/src/lib/",
+                exportingProduct.sourceDirectory + "/src/lib/",
+                exportingProduct.sourceDirectory + "/autogenerated/src/lib/",
             ]
         }
     }