The vulnerability is not $('#plazoActual').text(), but the fact that you take that value from the page (probably editable by a user), and use it in $(). It is reported, because $() can create elements, and if it's created from concatenated user input, it allows for injection (xss).

At first sight this particular case does not seem vulnerable though, because $() above does not create an element, it is just a selector for an input field (the first character is a # and there is a space). I think this cannot be exploited in general, but jQuery was a long time ago with all kinds of vulnerabilities also depending on the exact version. Also the input can potentially be manipulated so the selector finds something else in the page, which might be useful in a more complex attack.

A more robust and more secure way would be to find all inputs in #plazo (something like $('#plazo input')), iterate through them, and set checked where the value is $('#plazoActual').text(). So the point is to not have dynamic content in the selector.