another try to fix the bug

src/tjts5901/templates/base.html

@@ -6,6 +6,9 @@
     <meta charset="utf-8">
     <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
 
+    <!-- Upgrade http requests to https -->
+    <meta http-equiv="Content-Security-Policy" content="upgrade-insecure-requests">
+
     <!-- Bootstrap CSS -->
     <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap@4.6.2/dist/css/bootstrap.min.css" integrity="sha384-xOolHFLEh07PJGoPkLv1IbcEPTNtaed2xpHsD9ESMhqIYd0nLMwNLD69Npy4HI+N" crossorigin="anonymous">