You can create a Gist on GitHub and embed it on your web page: embedding Gists.
This is an example of a randomly chosen Gist: tap.groovy
.
Is embedding also possible with other code files from GitHub, for example with this randomly chosen C# file ICommand.cs
which is not a Gist?
One could just fetch
the file to embed on one's website.
fetch("https://raw.githubusercontent.com/Ayanmullick/test/master/AutomationAcc/test1.ps1")
.then(response => response.text())
.then(data => document.getElementById('code').textContent = data)
<pre id="code"></pre>