mariadb: fix post-installation script

See https://github.com/termux/termux-packages/issues/3713

packages/mariadb/build.sh

@@ -89,7 +89,7 @@ termux_step_create_debscripts() {
 	echo "if [ ! -e "$TERMUX_PREFIX/var/lib/mysql" ]; then" > postinst
 	echo "  echo 'Initializing mysql data directory...'" >> postinst
 	echo "  mkdir -p $TERMUX_PREFIX/var/lib/mysql" >> postinst
-	echo "  $TERMUX_PREFIX/bin/mysql_install_db --user=$(whoami) --datadir=$TERMUX_PREFIX/var/lib/mysql --basedir=$TERMUX_PREFIX" >> postinst
+	echo "  $TERMUX_PREFIX/bin/mysql_install_db --user=\$(whoami) --datadir=$TERMUX_PREFIX/var/lib/mysql --basedir=$TERMUX_PREFIX" >> postinst
 	echo "fi" >> postinst
 	echo "exit 0" >> postinst
 	chmod 0755 postinst