Adapt myid to zig 0.15.1

packages/myid/src/main.zig

@@ -67,7 +67,9 @@ pub fn main() !void {
     }
 
     if (show_help) {
-        const stderr = std.io.getStdErr().writer();
+        var buf: [4096]u8 = undefined;
+        var stderr_writer = std.fs.File.stderr().writer(&buf);
+        const stderr = &stderr_writer.interface;
         try stderr.print(
             \\Usage: myid [flags]
             \\
@@ -92,6 +94,7 @@ pub fn main() !void {
             .default_database_path = default.database_path,
             .default_socket_path = default.socket_path,
         });
+        try stderr.flush();
         return;
     }