Instead of setting the diagnostic value, now using push.

This is because Clang was complaining that the pop command at the
end of the file was not paired with a previous push command.

GaudiPython/src/Lib/AlgDecorators.cpp

@@ -22,7 +22,7 @@
 // Disable warnings on gcc
 // ============================================================================
 #if defined( __GNUC__ )
-#  pragma GCC diagnostic ignored "-Wdeprecated-declarations"
+#  pragma GCC diagnostic push ignored "-Wdeprecated-declarations"
 #endif
 // ============================================================================
 /** @file