gh-40797: Build metadata fixes 10.8.beta2
    
correct version constraints for pybind11, add gentoo package info  for
python-build

### 📝 Checklist

<!-- Put an `x` in all the boxes that apply. -->

- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
- [ ] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation and checked the documentation
preview.

### ⌛ Dependencies

<!-- List all open PRs that this PR logically depends on. For example,
-->
<!-- - #12345: short description why this is a dependency -->
<!-- - #34567: ... -->
    
URL: #40797
Reported by: Dima Pasechnik
Reviewer(s): Michael Orlitzky

Author: Release Manager

build/pkgs/pybind11/version_requirements.txt

@@ -1,2 +1,2 @@
-pybind11>=2.13.2,<2.14.0
+pybind11>=2.13.2
 # see https://github.com/scipy/scipy/blob/maintenance/1.15.x/pyproject.toml

build/pkgs/python_build/distros/gentoo.txt

@@ -0,0 +1 @@
+dev-python/build