DOCKER: Pin alpine build to Python 3.10

Currently, multidict and yarn fail to build from source and no 3.11 wheels are available.

Dockerfile

@@ -1,11 +1,11 @@
-FROM python:slim AS src
-RUN pip install build
+FROM python:3.10-slim AS src
+RUN pip install -U build pip
 RUN apt-get update && \
     apt-get install -y --no-install-recommends git
 COPY . /src/migas-server
 RUN python -m build /src/migas-server
 
-FROM python:slim
+FROM python:3.10-slim
 COPY --from=src /src/migas-server/dist/*.whl .
 ENV YARL_NO_EXTENSIONS=1 \
     MULTIDICT_NO_EXTENSIONS=1