object: Fix missing static_type_name template parameter
Regression from !867 (merged), only fails to build on 32-bit.
"error: use of deleted function ‘constexpr const char* Gjs::static_type_name() [with T = long unsigned int; GITypeTag TAG = GI_TYPE_TAG_VOID]’"
I'm guessing this is because of the different definitions of GType between 32-bit and 64-bit.