Plugin conflict with cc-scripts (or presumably any plugin or non-src script

I’m using the cc-scripts plugin to add some custom javascript to each page.

The plugin is old, but I don’t think that is particularly relevant.

It injects:

<script type="javascript">
  blah blah
</script>

into the page, and then speedup-javascript adds a:
<link rel="preload" href="1" as="script">

because wp_scripts is returning a src=1. The bug might not be in your plugin, but I haven’t found the source yet.