Add be

Thanks to Nicolas Müller
https://stacks.math.columbia.edu/tag/0A3R#comment-4186

etale-cohomology.tex

@@ -9942,7 +9942,7 @@ \section{M\'ethode de la trace}
 \begin{lemma}
 \label{lemma-pullback-filtered}
 Let $S$ be a connected scheme. Let $\ell$ be a prime number. Let
-$\mathcal{F}$ a finite type, locally constant sheaf of
+$\mathcal{F}$ be a finite type, locally constant sheaf of
 $\mathbf{F}_\ell$-vector spaces on $S_\etale$.
 Then there exists a finite \'etale morphism
 $f : T \to S$ of degree prime to $\ell$ such that $f^{-1}\mathcal{F}$