[main] Force an x64 runtime install

[github-actions]

Backport of #10494 to main

Works around an issue where because WPF uses Platform globally as to mean the Target platform, and because this is a default property that arcade uses to install additional runtimes, arcade installs the arm64 runtime on an x64 machine, which breaks when we try to run msbuild in signing. It would also break things if we ever ran testing.

<PropertyGroup>
    <Configuration Condition="'$(Configuration)' == ''">Debug</Configuration>
    <Platform Condition="'$(Platform)' == ''">AnyCPU</Platform>
    <PlatformName Condition="'$(PlatformName)' == ''">$(Platform)</PlatformName>
  </PropertyGroup>

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 11.25440%. Comparing base (83241ee) to head (8f4f7d2).

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #10525         +/-   ##
===================================================
+ Coverage   11.10049%   11.25440%   +0.15390%     
===================================================
  Files           3215        3215                 
  Lines         648440      648440                 
  Branches       71528       71528                 
===================================================
+ Hits           71980       72978        +998     
+ Misses        575464      574368       -1096     
- Partials         996        1094         +98     

Flag	Coverage Δ
Debug	11.25440% <ø> (+0.15390%)	⬆️

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