AvoidGlobalVars should only trigger on assignment

PowerShell classes requires variables to be initialized in a method before reference. This causes issues with global variables without scoping as the parser will throw a Variable is not assigned in the method error. To get around this the variable must be scoped but this causes PSScriptAnalyzer to throw a violation. The rule should only trigger when assigning a variable to the global scope not reading.

Steps to reproduce

class Test {
  [void] Abc() {
    if ($global:PSEdition -eq 'core') { write-host core }
  }
}

Expected behavior

No warnings

Actual behavior

RuleName                            Severity     ScriptName Line  Message
--------                            --------     ---------- ----  -------
PSAvoidGlobalVars                   Warning                 3     Found global variable 'global:PSEdition'.

If an unexpected error was thrown then please report the full error details using e.g. $error[0] | Select-Object *

Environment data

7.6-preview4

1.24.0

首先定位 PS AvoidGlobalVars 规则，并在 PowerShell 7.6-preview4 上重现 issue 中的 PowerShell 类示例。当读取 $global:PSEdition 不产生警告，而将变量赋值到全局作用域仍会触发该规则时，fix 即完成。