gh-140550: Use a bool for the Py_mod_gil value (GH-141519)

gh-140550: Use a bool for the Py_mod_gil value (GH-141519)

This needs a single bit, but was stored as a void* in the module
struct. This didn't matter due to packing, but now that there's
another bool in the struct, we can save a bit of memory by
making md_gil a bool.

Variables that changed type are renamed, to detect conflicts.