merge https://github.com/lightpanda-io/browser/pull/1275

src/TestHTTPServer.zig

@@ -132,6 +132,11 @@ fn getContentType(file_path: []const u8) []const u8 {
         return "text/xml";
     }
 
+    if (std.mem.endsWith(u8, file_path, ".mjs")) {
+        // mjs are ECMAScript modules
+        return "application/json";
+    }
+
     std.debug.print("TestHTTPServer asked to serve an unknown file type: {s}\n", .{file_path});
     return "text/html";
 }