Cleanup: use explicit casts when assigning booleans to floats

While valid, this isn't so common and cppcheck warns about this,
use explicit casts to suppress the warning, also correct "true"
being assigned to a float value.

source/blender/python/intern/bpy_driver.cc

@@ -633,7 +633,7 @@ float BPY_driver_exec(PathResolvedRNA *anim_rna,
           dvar->curval = float(PyLong_AsLong(driver_arg));
         }
         else if (PyBool_Check(driver_arg)) {
-          dvar->curval = (driver_arg == Py_True);
+          dvar->curval = float(driver_arg == Py_True);
         }
         else {
           dvar->curval = 0.0f;