scripts: Make checkShellScripts.sh error exit if it can't find src

Closes 31679.

scripts/maint/checkShellScripts.sh

@@ -31,6 +31,7 @@ TOPLEVEL=$(dirname "$(dirname "$HERE")")
 if [ ! -d "$TOPLEVEL/src" ]; then
     printf "Error: Couldn't find src directory in expected location: %s\\n" \
         "$TOPLEVEL/src"
+    exit 1
 fi
 
 # Check *.sh scripts, but ignore the ones that we can't fix