merge: Rewrite Dockerfile to use python:3.12

.github/actions/merge/Dockerfile

@@ -1,10 +1,24 @@
-FROM quay.io/fedora/fedora:38
+FROM python:3.12 AS builder
 
-RUN dnf install -y flatpak-builder git /usr/bin/pip && \
-    dnf clean all
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends \
+        libcairo2-dev libgirepository1.0-dev
 
-ADD requirements.txt /requirements.txt
-RUN pip install -r /requirements.txt
+ADD requirements.txt .
 
-ADD entrypoint.py /entrypoint.py
-ENTRYPOINT ["/entrypoint.py"]
+RUN python -m venv /venv && \
+    /venv/bin/python -m pip install -r requirements.txt
+
+FROM python:3.12-slim
+ENV PATH="/venv/bin:$PATH"
+
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends \
+        libcairo2 libgirepository-1.0-1 gir1.2-json-1.0 && \
+    apt-get clean && rm -rf /var/lib/apt/lists/*
+
+COPY --from=builder /venv /venv
+COPY . /app
+WORKDIR /app
+
+CMD ["/app/entrypoint.py"]