Script: Fix a syntax error (#40767)

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tools/build/build-installer.ps1

@@ -81,7 +81,7 @@ function RunMSBuild {
 
     $base = @(
         $Solution
-        "/p:Platform=`"$Platform`""
+        "/p:Platform=$Platform"
         "/p:Configuration=$Configuration"
         "/p:CIBuild=true"
         '/verbosity:normal'
@@ -158,4 +158,4 @@ RunMSBuild 'installer\PowerToysSetup.sln' "/m /t:PowerToysInstaller /p:PerUser=$
 
 RunMSBuild 'installer\PowerToysSetup.sln' "/m /t:PowerToysBootstrapper /p:PerUser=$PerUser"
 
-Write-Host '[PIPELINE] Completed'
+Write-Host '[PIPELINE] Completed'