* Update attr.h: fix a warning found by static code analyzer

Update attr.h: fix a warning found by Visual Studio static code analyzer

Severity:Warning
Code:C6323
Description: Use of arithmetic operator on Boolean type(s).
Location:	C:\src\onnxruntime\debug\pybind11\src\pybind11\include\pybind11\attr.h:547

* Update include/pybind11/attr.h

Co-authored-by: Henry Schreiner <HenrySchreinerIII@gmail.com>

* Update attr.h

Co-authored-by: Henry Schreiner <HenrySchreinerIII@gmail.com>