Fix referencing of cairo_t returned from wxDCImpl::GetCairoContext().

It was assumed that all callers were going to unref the cairo_t, but that is not
true, so callers that are going to unref it should ref it themselves.
See #15455


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74746 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/print.cpp

@@ -1209,7 +1209,7 @@ bool wxGtkPrinterDCImpl::IsOk() const
 
 void* wxGtkPrinterDCImpl::GetCairoContext() const
 {
-    return (void*) cairo_reference( m_cairo );
+    return m_cairo;
 }
 
 void* wxGtkPrinterDCImpl::GetHandle() const