It's not from any of Plato's works that we know of, in any case.

I like the sentiment, though.

of the attribution. You are quite likely correct.

Plato was dissatisfied with rulers who lacked knowledge and moral strength to act according to the common good – in other words, rulers motivated by self-interest were not strong leaders.
Only philosophers are morally and intellectually suited to govern and lead. Morally because they are interested in and have a passion for truth and learning, while showing no interest in the temptations of gaining power for the sake of power. Intellectually because they are able to attain knowledge on the ideal forms of virtue, beauty, and the good.
https://www.cityu.edu/blog/what-plato-can-teach-us-about-leadership-part-1-of-2/