Update HTMx to version 1.9.0

I mainly did it for the new hx-on attribute, to click the update
button on recompute, but it does not seem to work as i think it does.
Anyway, there are some fixed bugs.

From the release announcement[0]:

## New Features

  * Support for view transitions, based on the experimental View
    Transitions API currently available in Chrome 111+ and coming to
    other browsers soon.
  * Support for “naked” hx-trigger attributes, where an hx-trigger is
    present on an element that does not have an hx-get, etc. defined on
    it. Instead, it will trigger the new htmx:triggered event, which
    can be responded to via your preferred scripting solution.
  * Support for generalized inline event handling via the new hx-on
    attribute, which addresses the shortcoming of limited onevent
    properties attributes in HTML.

## Improvements & Bug fixes

  * A memory leak fix by @croxton

[0]: https://htmx.org/posts/2023-04-11-htmx-1-9-0-is-released/

web/template/app.gohtml

@@ -5,7 +5,7 @@
 		<meta name="viewport" content="width=device-width, initial-scale=1">
 		<title>{{ template "title" . }} — Numerus</title>
 		<link rel="stylesheet" type="text/css" media="screen" href="/static/numerus.css">
-		<script src="/static/htmx@1.8.6.min.js"></script>
+		<script src="/static/htmx@1.9.0.min.js"></script>
 		<script type="module" src="/static/numerus.js"></script>
         <script defer src="/static/alpinejs@3.12.0.min.js"></script>
 	</head>