fix: remove backtick from valid password characters (#15756)

Since backticks are the PowerShell escape character, they are silently
consumed. To actually use backticks, they would need to be doubled when
used.

This change increases the safety of generated passwords for other
terraform modules that might use this value unawares.

examples/templates/azure-windows/main.tf

@@ -65,9 +65,9 @@ resource "random_password" "admin_password" {
   length  = 16
   special = true
   # https://docs.microsoft.com/en-us/windows/security/threat-protection/security-policy-settings/password-must-meet-complexity-requirements#reference
-  # we remove characters that require special handling in XML, as this is how we pass it to the VM
-  # namely: <>&'"
-  override_special = "~!@#$%^*_-+=`|\\(){}[]:;,.?/"
+  # we remove characters that require special handling in XML, as this is how we pass it to the VM; we also remove the powershell escape character
+  # namely: <>&'`"
+  override_special = "~!@#$%^*_-+=|\\(){}[]:;,.?/"
 }
 
 locals {