Fix os.execute stderr redirection

Closes #20986

vlib/os/os_nix.c.v

@@ -339,10 +339,7 @@ pub fn mkdir(path string, params MkdirParams) ! {
 // execute starts the specified command, waits for it to complete, and returns its output.
 @[manualfree]
 pub fn execute(cmd string) Result {
-	// if cmd.contains(';') || cmd.contains('&&') || cmd.contains('||') || cmd.contains('\n') {
-	// return Result{ exit_code: -1, output: ';, &&, || and \\n are not allowed in shell commands' }
-	// }
-	pcmd := if cmd.contains('2>') { cmd.clone() } else { '${cmd} 2>&1' }
+	pcmd := 'exec 2>&1;${cmd}'
 	defer {
 		unsafe { pcmd.free() }
 	}

vlib/os/os_test.c.v

@@ -907,6 +907,16 @@ fn test_execute_with_stderr_redirection() {
 	assert os.exists(stderr_path)
 }
 
+fn test_execute_with_linefeeds() {
+	if os.user_os() == 'windows' {
+		return
+	}
+	result := os.execute('true\n')
+	assert result.exit_code == 0
+	result2 := os.execute('false\n')
+	assert result2.exit_code == 1
+}
+
 fn test_command() {
 	if os.user_os() == 'windows' {
 		eprintln('>>> os.Command is not implemented fully on Windows yet')