Add Windows ARM64 support to CI

[chinazhangchao]

Hi @dvarrazzo , I'm from Microsoft and recently I'm working on improving Python ecosystem support for Windows on Arm.
So I updates the CI workflows to add support for Windows ARM64 builds and tests. Could you please help to review? Thanks.

Test results:
https://github.com/chinazhangchao/psycopg2/actions/runs/32325062129

Windows ARM64 support and workflow updates:

• Updated the windows job in .github/workflows/packages.yml to add win_arm64 to the build matrix, conditionally select the appropriate runner image, and exclude unsupported Python versions for ARM64.
• Modified PostgreSQL setup in the workflow to install it only if not present, accommodating the lack of PostgreSQL on Windows ARM64 runners.
• Adjusted environment variables and paths to use the correct vcpkg triplet (arm64-windows for ARM64, x64-windows-release for AMD64) and set CIBW_ARCHS_WINDOWS accordingly. [1] [2]

Build script improvements:

• Updated scripts/build/wheel_win32_before_build.bat to set VCPKG_TARGET_TRIPLET based on architecture and install the correct libpq package for each triplet.

Stub script enhancements:

• Enhanced pg_config_vcpkg_stub to support both AMD64 and ARM64, checking the platform and triplet, and constructing the vcpkg path dynamically. The documentation was also updated to reflect the new usage. [1] [2]

[ndabas]

@chinazhangchao Skipping tests would be a bad idea. You can install PostgreSQL on the WoA runners like I have done in this PR: psycopg/psycopg#1385