Fix requirements.txt install in python3 devcontainer

Author: qubitron

containers/python-3/.devcontainer/Dockerfile

@@ -14,6 +14,9 @@ RUN apt-get update && apt-get -y install git procps
 # Install any missing dependencies for enhanced language service
 RUN apt-get install -y libicu[0-9][0-9]
 
+RUN mkdir /workspace
+WORKDIR /workspace
+
 # Install Python dependencies from requirements.txt if it exists
 COPY .devcontainer/requirements.txt.temp requirements.txt* /workspace/
 RUN if [ -f "requirements.txt" ]; then pip install -r requirements.txt && rm requirements.txt*; fi