🚨(docker) fix docker warning about casing

When we build the docker image, we get a warning
about the casing in the Dockerfile. This commit
fixes the casing in the Dockerfile.

Dockerfile

@@ -1,7 +1,7 @@
 # Django impress
 
 # ---- base image to inherit from ----
-FROM python:3.12.6-alpine3.20 as base
+FROM python:3.12.6-alpine3.20 AS base
 
 # Upgrade pip to its latest release to speed up dependencies installation
 RUN python -m pip install --upgrade pip setuptools
@@ -11,7 +11,7 @@ RUN apk update && \
   apk upgrade
 
 # ---- Back-end builder image ----
-FROM base as back-builder
+FROM base AS back-builder
 
 WORKDIR /builder
 
@@ -23,7 +23,7 @@ RUN mkdir /install && \
 
 
 # ---- mails ----
-FROM node:20 as mail-builder
+FROM node:20 AS mail-builder
 
 COPY ./src/mail /mail/app
 
@@ -34,7 +34,7 @@ RUN yarn install --frozen-lockfile && \
 
 
 # ---- static link collector ----
-FROM base as link-collector
+FROM base AS link-collector
 ARG IMPRESS_STATIC_ROOT=/data/static
 
 # Install pango & rdfind
@@ -59,7 +59,7 @@ RUN DJANGO_CONFIGURATION=Build DJANGO_JWT_PRIVATE_SIGNING_KEY=Dummy \
 RUN rdfind -makesymlinks true -followsymlinks true -makeresultsfile false ${IMPRESS_STATIC_ROOT}
 
 # ---- Core application image ----
-FROM base as core
+FROM base AS core
 
 ENV PYTHONUNBUFFERED=1
 
@@ -97,7 +97,7 @@ WORKDIR /app
 ENTRYPOINT [ "/usr/local/bin/entrypoint" ]
 
 # ---- Development image ----
-FROM core as backend-development
+FROM core AS backend-development
 
 # Switch back to the root user to install development dependencies
 USER root:root
@@ -123,7 +123,7 @@ ENV DB_HOST=postgresql \
 CMD ["python", "manage.py", "runserver", "0.0.0.0:8000"]
 
 # ---- Production image ----
-FROM core as backend-production
+FROM core AS backend-production
 
 ARG IMPRESS_STATIC_ROOT=/data/static