You have copper pipes. As such, if you can find "copper wool" in your area, I'd use that.
Mice can chew through wood, plastic, drywall, foam insulation, just about anything not made of metal. Using something like steel wool or copper wool makes it easy to stuff into narrow spots like you have shown here, and they cannot (or are unwilling to) chew through that.
The reason I suggest "copper wool" instead of "steel wool" is that there is such a thing as "dissimilar metal corrosion". When copper and steel come in contact, the metals in one of the two will corrode at a faster rate than if they were not in contact. So to be on the safe side, i'd use copper wool next to copper pipes, even though I believe it is the steel that would corrode more quickly, not the copper.
If it is just for a short period, no problem. Use steel wool as it is probably cheaper and easier to find. But short term fixes tend to become long term solutions for some landlords. And that's why I recommend a solution that won't potentially introduce new issues in the future.