Update testapp/Dockerfile

testapp/Dockerfile

 FROM python:3.10.4-alpine
 RUN apk --update add bash nano
+RUN python3 && py3-pip  
+RUN pip install flask
 COPY main.py /testapp/
-COPY requirements.txt /testapp/
-RUN pip install -r /testapp/requirements.txt
 CMD python3 testapp/main.py
 EXPOSE 5000