Support for matrix.os about github-workflow-plugin

[mhorioka]

@YunaBraska thank you for your confirmation!

• I had an impression that highlighting does not work because I don't see any green colored text. But seems like it gets green for quoted literals only. So works as expected
• I expected not only highlighting but also code completion for "matrix.os". If it's not supported now, then it's ok.

[YunaBraska]

Cool, I will add matrix.os on my list to implement 👍

[YunaBraska]

What issue do you have? The Plugin seems to be loaded as far as I can see from your screenshot. The GitHub icons are on the files, and the syntax highlighting started to underline and mark the actions to make them clickable. Next to it, you have a refresh button in case the action has some issues. I probably have no highlighting for matrix.os that's right. But when you misspell something like in your var ${{steps.npm-cache.outputs.dir}}, it should be highlighted then, and also it should give you code completion