Fix Mattermost link generation on Matrix page

content/u/products/hosted-matrix-chat/contents.lr

@@ -170,10 +170,10 @@ on our <a href="https://redmine.ungleich.ch/projects/open-infrastructure/wiki/Un
 </p>
 
 <div class="alert alert-secondary">
-You might be also interested in our [Mattermost-based chat
-offer](../zero-carbon-chat), which might be closer to what you expect for a
-enterprise team chat at the moment. We use both at ungleich, since Matrix is
-especially convenient to reach out to the world!
+You might be also interested in our <a
+href="../zero-carbon-chat">Mattermost-based chat offer</a>, which might be
+closer to what you expect for a enterprise team chat at the moment. We use both
+at ungleich, since Matrix is especially convenient to reach out to the world!
 </div>
 
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