fix(post-install): export GZIP in pigz wrapper so level -1 takes effect

The wrapper assigned GZIP="-1" without exporting it, so pigz never saw
it and compressed at its default level 6. Export it, and refresh
/bin/gzip on re-runs when gzip.original already exists so existing
installs pick up the corrected wrapper.

scripts/post_install/customizable_post_install.sh

@@ -1666,14 +1666,14 @@ configure_pigz() {
     if [ ! -f /bin/pigzwrapper ] || ! cmp -s /bin/pigzwrapper - <<EOF
 #!/bin/sh
 PATH=/bin:\$PATH
-GZIP="-1"
+export GZIP="-1"
 exec /usr/bin/pigz "\$@"
 EOF
     then
         pmx_write_file /bin/pigzwrapper <<EOF
 #!/bin/sh
 PATH=/bin:\$PATH
-GZIP="-1"
+export GZIP="-1"
 exec /usr/bin/pigz "\$@"
 EOF
         chmod +x /bin/pigzwrapper
@@ -1689,6 +1689,10 @@ EOF
         pmx_write_file /bin/gzip < /bin/pigzwrapper && \
         chmod +x /bin/gzip
         msg_ok "$(translate "gzip replaced with pigz wrapper successfully")"
+    elif ! cmp -s /bin/gzip /bin/pigzwrapper; then
+        pmx_write_file /bin/gzip < /bin/pigzwrapper && \
+        chmod +x /bin/gzip
+        msg_ok "$(translate "gzip replaced with pigz wrapper successfully")"
     else
         msg_ok "$(translate "gzip replaced with pigz wrapper successfully")"
     fi