Fix build with poppler-26.05.

From svn r27545.

Index: scribus/plugins/import/pdf/importpdfconfig.h
--- scribus/plugins/import/pdf/importpdfconfig.h.orig
+++ scribus/plugins/import/pdf/importpdfconfig.h
@@ -21,4 +21,8 @@ for which a new license (GPL+exception) is in place.
 #define POPPLER_CONST_25_02
 #endif
 
+#if POPPLER_ENCODED_VERSION >= POPPLER_VERSION_ENCODE(26, 5, 0)
+using SplashCoord = double;
+#endif
+
 #endif
