fix Dockerfile build.

The `alpine:latest` image do not longer include php83 on their repos.
Using a specific image tag is better to prevent breakages on the future.

Ref: https://github.com/dnaprawa/dockerfile-best-practices?tab=readme-ov-file#the-latest-is-an-evil-choose-specific-image-tag

Dockerfile

@@ -1,8 +1,8 @@
-FROM alpine:latest
+FROM alpine:3.21
 WORKDIR /var/www/html/4get
 
 RUN apk update && apk upgrade
-RUN apk add php apache2-ssl php83-fileinfo php83-openssl php83-iconv php83-common php83-dom php83-sodium php83-curl curl php83-pecl-apcu php83-apache2 imagemagick php83-pecl-imagick php-mbstring imagemagick-webp imagemagick-jpeg
+RUN apk add php apache2-ssl php84-fileinfo php84-openssl php84-iconv php84-common php84-dom php84-sodium php84-curl curl php84-pecl-apcu php84-apache2 imagemagick php84-pecl-imagick php84-mbstring imagemagick-webp imagemagick-jpeg
 
 COPY . .
 
@@ -14,4 +14,4 @@ EXPOSE 443
 ENV FOURGET_PROTO=http
 
 ENTRYPOINT  ["./docker/docker-entrypoint.sh"]
-CMD ["start"]
+CMD ["start"]