Draft: Add note on ConstrainedLanguage Mode

What does this MR do?

Customer has opened an issue Powershell executor not compatible with Constra... (#38899) where they were getting the following error when the runner attempts to clone the repo:

Getting source from Git repository
...
Cannot invoke method. Method invocation is supported only on core types in this language mode.
At line:369 char:1
+ [System.IO.File]::WriteAllText("c:\GitLab Runner\builds\t2_LiXSTk\0\o ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [], RuntimeException
    + FullyQualifiedErrorId : MethodInvocationNotSupportedInConstrainedLanguage

This Docs MR is to clarify that powrshell's ConstrainedLanguage Mode is not supported with GitLab Runners.

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What are the relevant issue numbers?