Just the ampersand, without the redirection?

scripts/build.sh

@@ -4,7 +4,7 @@
 necessary_packages=("pdflatex")
 
 for package in "${necessary_packages}"; do
-    if ! [dpkg -l "${package}" > /dev/null 2>&1 &]; then
+    if ! [dpkg -l "${package}" > /dev/null &]; then
         echo "Error: ${package} is not installed."
         exit 1
     fi