Fixes for php extension installer

debian/Dockerfile

@@ -19,7 +19,7 @@ FROM dunglas/frankenphp:1-php8.3-bookworm
 ARG user=ninja
 
 # PHP modules
-ARG php_require="bcmath gd pdo_mysql zip"
+ARG php_require="bcmath gd pdo_mysql zip mbstring"
 ARG php_suggest="exif imagick intl pcntl soap saxon-12.5.0"
 ARG php_extra="opcache"
 
@@ -61,11 +61,14 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     && rm -rf /var/lib/apt/lists/*
 
 # Install PHP extensions
+COPY --from=ghcr.io/mlocati/php-extension-installer /usr/bin/install-php-extensions /usr/local/bin/
+
 RUN install-php-extensions \
     ${php_require} \
     ${php_suggest} \
     ${php_extra}
 
+
 # Configure PHP
 RUN ln -s "${PHP_INI_DIR}/php.ini-production" "${PHP_INI_DIR}/php.ini"