Highlight powershell with correct syntax

Author: Silex

src/pages/how-to/troubleshooting-client.mdx

@@ -279,7 +279,7 @@ netbird service stop
 In case you need to configure environment variables, you need to add them as system variables so they get picked up by
 the agent on the next psexec run:
 
-```shell
+```powershell
 [Environment]::SetEnvironmentVariable("PIONS_LOG_DEBUG", "all", "Machine")
 ````