Change image to python:3.9

Dockerfile

@@ -1,21 +1,17 @@
-FROM ubuntu:20.04
+FROM python:3.9
 
 WORKDIR /code
 
+ENV SYSTEM=spaces
+
 COPY ./requirements.txt /code/requirements.txt
 
 # Preconfigure tzdata
 RUN DEBIAN_FRONTEND="noninteractive" apt-get -qq update && \
     DEBIAN_FRONTEND="noninteractive" apt-get install -y tzdata
 
-# Add deadsnakes PPA to get Python 3.9
-RUN apt-get install -y software-properties-common && \
-    add-apt-repository ppa:deadsnakes/ppa && \
-    apt-get update && \
-    apt-get install -y python3.9 python3-pip
-
 RUN apt-get update -qq && \
-    apt-get install -qq build-essential libasound2-dev libjack-dev wget cmake pkg-config libglib2.0-dev ffmpeg
+    apt-get install -qq python3-pip build-essential libasound2-dev libjack-dev wget cmake pkg-config libglib2.0-dev ffmpeg
 
 # Download libfluidsynth source
 RUN wget https://github.com/FluidSynth/fluidsynth/archive/refs/tags/v2.3.3.tar.gz && \
@@ -42,8 +38,7 @@ USER user
 
 # Set home to the user's home directory
 ENV HOME=/home/user \
-    PATH=/home/user/.local/bin:$PATH \
-    SYSTEM='spaces'
+    PATH=/home/user/.local/bin:$PATH
 
 # Set the working directory to the user's home directory
 WORKDIR $HOME/app