Starting with the New York release, the Script Editor (used in Script Includes, ACLs, etc) gives warnings when it detects a combination of tabs and spaces in code. However, there are instances where mixing tabs and spaces is appropriate, like object / hash-map notation where center justification around the : makes for easier reading.
The warning message is working as expected. With that said, while it is not recommended, you can turn off the default Eslint recommended rules, including the 'no-mixed-spaces-and-tabs' rule by doing the following:
1) Navigate to Filter Navigator and type sys_properties.list
2) In the System Properties list view, search for the 'glide.ui.syntax_editor.linter.eslint_config' system property, and open the record
3) In the 'Value' section, navigate to the line: "no-mixed-spaces-and-tabs": "warn",
4) Change line to: "no-mixed-spaces-and-tabs": "off",
5) Save or Update the record.