Latex Warning After Update Miktex: Font shape `T1/lmr/m/scit' undefined (Font) using `T1/lmr/m/scsl' instead

In older LaTeX versions mixing small caps (scshape, textsc) and italic (itshape, textit) didn't really worked. The commands cancelled each other out, you only got the one or the other:

documentclass{article}
usepackage[T1]{fontenc}
usepackage{lmodern}
begin{document}
{scshapeitshape abc} {itshapescshape abc}
end{document}

gives e.g. in texlive 2018

In newer LaTeX the font handling has been improved here. Now LaTeX tries to combine the two shapes. But lmodern has no small caps + italic shape, so LaTeX falls back to small caps + slanted:

And that is what the message is telling you: that instead of scit (small caps and italic) it will use scsl (small caps and slanted). If this fine for you you can safely ignore the message.