make.ps1: Run-IntegrationTests(): set working directory for test suite

This function changed to the correct working directory before starting the tests
(which is the same as on Linux), however the `ProcessStartInfo` process does
not inherit this working directory, which caused Windows tests to be running
with a different working directory as Linux (causing files used in tests to not
be found).

From the documentation; https://docs.microsoft.com/en-us/dotnet/api/system.diagnostics.processstartinfo.workingdirectory?view=netframework-4.8

> When `UseShellExecute` is `true`, the fully qualified name of the directory that contains
> the process to be started. When the `UseShellExecute` property is `false`, the working
> directory for the process to be started. The default is an empty string (`""`).

This patch sets the `ProcessStartInfo.WorkingDirectory` to the correct working
directory before starting the process.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit 6ae46aeabf056180067dd6af8d5d8588d6075c31)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

hack/make.ps1

@@ -343,6 +343,7 @@ Function Run-IntegrationTests() {
         Write-Host "Running $($PWD.Path)"
         $pinfo = New-Object System.Diagnostics.ProcessStartInfo
         $pinfo.FileName = "$($PWD.Path)\test.exe"
+        $pinfo.WorkingDirectory = "$($PWD.Path)"
         $pinfo.RedirectStandardError = $true
         $pinfo.UseShellExecute = $false
         $pinfo.Arguments = $env:INTEGRATION_TESTFLAGS