tests: test.sh: utilize $BIN

tests/test.sh

@@ -31,7 +31,7 @@ done
 printf "Starting POSIX compatibility testing.\n\n"
 
 for test in tests/posix/*.sh; do
-	export PATH="build/bin:$PATH"
+	export PATH="$BIN:$PATH"
 	printf '%s: %s: Testing utility.\n' "$0" "$test"
 	"$utility"
 	printf '\n'