fix: force stdin to Stdio::null for all user code execution (#6575)

Set stdin to Stdio::null for all Commands that execute user code across all supported languages to prevent unwanted input consumption. This affects Python, Deno, Bash, PowerShell, Go, Rust, PHP, Ruby, Java, C#, Ansible, Nu, and Bun executors.

The dedicated worker handler was intentionally left unchanged as it requires stdin for inter-process communication.

Co-authored-by: claude[bot] <209825114+claude[bot]@users.noreply.github.com>
Co-authored-by: windmill-internal-app[bot] <windmill-internal-app[bot]@users.noreply.github.com>

backend/windmill-worker/src/java_executor.rs

@@ -689,6 +689,7 @@ async fn run<'a>(
             }
         }
         cmd.args(&["-classpath", &classpath, "net.script.App"])
+            .stdin(Stdio::null())
             .stdout(Stdio::piped())
             .stderr(Stdio::piped());