Use vswhere to locate VS install in 32-bit Windows CI (#2442)

The hosted windows-latest runner is migrating from VS 2022 to VS 2026
(NOTICE: windows-2025 -> windows-2025-vs2026 by 2026-05-12). The
hardcoded path C:\Program Files\Microsoft Visual Studio\2022\Enterprise
no longer exists on the new image, so vcvarsall.bat silently fails and
'cl' is not on PATH.

Resolve the install path via vswhere.exe (stable location, version
agnostic) and exit if vcvarsall.bat fails so future breakage surfaces
immediately instead of as a confusing 'cl not recognized' error.

.github/workflows/test-32bit.yml

@@ -21,7 +21,8 @@ jobs:
       - name: Build (Win32)
         shell: cmd
         run: |
-          call "C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Auxiliary\Build\vcvarsall.bat" x86
+          for /f "usebackq tokens=*" %%i in (`"%ProgramFiles(x86)%\Microsoft Visual Studio\Installer\vswhere.exe" -latest -property installationPath`) do set VSDIR=%%i
+          call "%VSDIR%\VC\Auxiliary\Build\vcvarsall.bat" x86 || exit /b 1
           cl /std:c++14 /EHsc /W4 /WX /c /Fo:NUL test\test_32bit_build.cpp
 
   test-arm32: