Being able to run tests by setting $PsModulePath instead of XCopy to one of those folders

As discussed internally. Instead of doing a Copy-Item of the PSScriptAnalyer folder in the out folder to the first $env:PSModulePath folder (where it can override an existing installation due to the version number being the same), we should just be able to just set add the out folder to the beginning of the $env:PSModulePath variables during test execution. However, this does not even work for Windows PowerShell at the moment due to the LibraryUsageTests (I get one failure here).

从复制 out 文件夹中的 PSScriptAnalyzer 文件夹的测试设置，以及 Tests/Engine/LibraryUsage.tests.ps1 第 214 行的失败开始。重现 Windows PowerShell 的失败，然后验证测试执行使用位于 $env:PSModulePath 开头的 out 文件夹，并且无需复制模块测试套件即可通过。