Bump composer version + php8

Author: jekkos

Dockerfile

@@ -1,10 +1,10 @@
-FROM php:7.4.3-alpine
+FROM php:8-alpine
 
 COPY --from=composer /usr/bin/composer /usr/bin/composer
 
 ENV COMPOSER_ALLOW_SUPERUSER=1
 ENV COMPOSER_HOME=/tmp
-ENV COMPOSER_VERSION=1.9.3
+ENV COMPOSER_VERSION=2.5.8
 
 RUN apk add zlib-dev libpng-dev libzip-dev icu-dev oniguruma-dev
 RUN docker-php-ext-install gd zip intl mbstring