phpMyAdmin stable (5.1.0.) fails on mime type check with messages.php

Question

After deploying the downloaded phpMyAdmin stable (5.1.0) to App Engine using php 7, the main UI (i.e. the view after login) becomes unresponsive, apparently due to the following javascript error in the browser:

Refused to execute script from '{App Engine app URL}/js/messages.php?l=en&v=5.1.0' because its MIME type ('text/html') is not executable, and strict MIME type checking is enabled.

This also causes several JS errors afterwards:

Uncaught ReferenceError: Messages is not defined

How to retain the correct text/javascript MIME type header (that the messages.php file actually tries to set)?

The MIME types are correct when run on localhost, so apparently there is something that makes App Engine change them for messages.php (perhaps due to that file being called as script in the html code?).

Handlers in app.yaml, as adjusted to php 7 from Google's tutorial for php 5:

handlers:
  - url: /(.+\.(ico|jpg|png|gif))$
    static_files: \1
    upload: (.+\.(ico|jpg|png|gif))$

  - url: /(.+\.(htm|html|css|js))$
    static_files: \1
    upload: (.+\.(htm|html|css|js))$

  - url: /(.+\.php)$
    script: auto
    secure: always

Answer 1

To make phpMyAdmin work on GoogleAppEngine please follow the solution I crafted: https://github.com/phpmyadmin/phpmyadmin/issues/16922