As far as I know when it comes to HTML, it’s always been double-quotes, whether you are using them to link an external css or js files to your document even an image. I don’t think there is any “standards” when it comes to double or single quotes on attributes. But I’ve used different sources and platforms to learn HTML, for example on w3schools they teach you that the syntax for an image is :
<img src=" url " alt=" alternate text ">
Another fact is that most browsers use double quotes by default. While single quotes might work most of the time, I believe its good practice to use double-quotes when writing HTML.