fix(ci): Work around unset VCToolsRedistDir environment variable

Recently, the "vcvarsall.bat" batch script from VS 2019 has stopped
defining the VCToolsRedistDir environment variable, for reasons unknown
so far [1].

We rely on that variable in CI to copy MSVC runtime DLLs to our Windows
packages, so this adds a workaround for when that variable is not set.

[1] actions/runner-images#10819

.github/workflows/windows.yml

@@ -135,6 +135,10 @@ jobs:
 
           # Include MSVC 2019 runtime libraries.
           if ('${{ matrix.build-type }}' -ieq 'release') {
+              if ($env:VCToolsRedistDir -eq $null) {
+                  # XXX: Hack to work around this issue: https://github.com/actions/runner-images/issues/10819
+                  $env:VCToolsRedistDir = -join ($env:VCINSTALLDIR, "Redist\MSVC\", $env:VCToolsVersion, "\")
+              }
               Copy-Item $env:VCToolsRedistDir\${{ matrix.arch }}\Microsoft.VC142.CRT\msvcp140.dll
               Copy-Item $env:VCToolsRedistDir\${{ matrix.arch }}\Microsoft.VC142.CRT\msvcp140_1.dll