Mime type of .gif asset files are not updated

[doekenorg]

Describe the bug
Screenshots can be .gif files. These are useful for showing the interaction the user can expect. The mime-type of .gif files is not updated. So the file will be downloaded, instead of shown in the browser.

Steps to Reproduce

1. Create a repo with an assets folder that contains a .gif file
2. Run the action
3. Click the screenshot in the WordPress plugin page

Expected behavior
The file will open in the browser.

Additional context
PR added.

[jeffpaul]

Note that WP.org only states support for PNG or JPG filetypes for screenshots: https://developer.wordpress.org/plugins/wordpress-org/plugin-assets/#filenames-3. Also, they do not state support for GIF for any plugin asset type for that matter.

[doekenorg]

Sorry, working in my phone now and accidentally clicked the closing button.

It is pretty tucked away, but you can find a reference to this in the readme example. https://developer.wordpress.org/plugins/wordpress-org/how-your-readme-txt-works/#example-readme

This is how I found it was possible.