ci(dockerfile): bump PHP to 8.4 to match utopia-php/client requirement

utopia-php/client uses PHP 8.4's "method-call on new expression"
syntax (e.g. `new Request($method, $uri)->withUri(...)`). PHP 8.3
parses this as `unexpected token "->" expecting ";"` — the Tests job
was failing with 129 ParseErrors across the suite as a result.

Bumps the final stage image to php:8.4-cli-alpine. composer.json
already declares >=8.4 since the lib swap.

Author: lohanidamodar

Dockerfile

@@ -8,7 +8,7 @@ COPY composer.json /src/
 RUN composer install --ignore-platform-reqs --optimize-autoloader \
     --no-plugins --no-scripts --prefer-dist
 
-FROM php:8.3.3-cli-alpine3.19 as final
+FROM php:8.4-cli-alpine as final
 
 LABEL maintainer="team@appwrite.io"