Fix Windows+macOS CI by updating to Python 3.11.

[ScottTodd]

Pending CI builds (since these are nightly / on-demand and take hours):

• Windows: https://github.com/iree-org/iree/actions/runs/11689195978
• macOS: https://github.com/iree-org/iree/actions/runs/11689197108

The new iree.build package depends on Python 3.11: #18630 (comment). We currently publish Python packages for 3.9+ on Linux but only 3.11+ on macOS and Windows:

• iree/build_tools/python_deploy/build_linux_packages.sh

  Line 68 in 9650bfe

  python_versions="${override_python_versions:-cp39-cp39 cp310-cp310 cp311-cp311 cp312-cp312 cp313-cp313 cp313-cp313t}"

• iree/.github/workflows/build_package.yml

  Lines 259 to 266 in 9650bfe

  	- name: Build compiler wheels (Windows)
  	if: "matrix.build-package == 'py-compiler-pkg' && matrix.build-family == 'windows'"
  	shell: powershell
  	env:
  	package_suffix: ${{ github.event.inputs.package_suffix }}
  	packages: "iree-compiler"
  	output_dir: "${{ github.workspace }}/bindist"
  	override_python_versions: "3.11 3.12 3.13"

• iree/.github/workflows/build_package.yml

  Lines 247 to 254 in 9650bfe

  	- name: Build compiler wheels (MacOS)
  	if: "matrix.build-package == 'py-compiler-pkg' && matrix.build-family == 'macos'"
  	shell: bash
  	env:
  	package_suffix: ${{ github.event.inputs.package_suffix }}
  	packages: "iree-compiler"
  	output_dir: "${{ github.workspace }}/bindist"
  	override_python_versions: "3.11 3.12 3.13"

We can relax the 3.11 dependency in the package, but we might as well update these workflows to test with the version that we distribute packages for.

[marbre]

Thanks Scott!

[ScottTodd]

macOS build passed.

Windows build is still pending but looks good so far. I'll wait for it to complete before merging.