chore: Update CI workflow to install Python 3.12 using pyenv

This commit modifies the CI workflow to install Python 3.12 using pyenv instead of the default package manager. This change is necessary as Debian Bullseye does not provide Python 3.12 in its default repositories. The updated installation process includes necessary dependencies and ensures that the correct version of Python is set globally for the build environment.

.gitea/workflows/ci.yml

@@ -419,10 +419,23 @@ jobs:
 
       - name: Validate backend (imports and app instantiation)
         run: |
-          # Install Python 3.12 (required for modern type hints like str | None)
-          apt-get update && apt-get install -y software-properties-common
-          add-apt-repository -y ppa:deadsnakes/ppa
-          apt-get update && apt-get install -y python3.12 python3.12-venv python3.12-dev
+          # Install Python 3.12 using pyenv (required for modern type hints like str | None)
+          # Debian Bullseye doesn't have Python 3.12 in default repos, so we use pyenv
+          apt-get update && apt-get install -y \
+            make build-essential libssl-dev zlib1g-dev \
+            libbz2-dev libreadline-dev libsqlite3-dev wget curl llvm \
+            libncursesw5-dev xz-utils tk-dev libxml2-dev libxmlsec1-dev \
+            libffi-dev liblzma-dev git
+          
+          # Install pyenv
+          export PYENV_ROOT="/opt/pyenv"
+          export PATH="$PYENV_ROOT/bin:$PATH"
+          curl https://pyenv.run | bash
+          
+          # Install Python 3.12 using pyenv
+          eval "$(pyenv init -)"
+          pyenv install -v 3.12.7
+          pyenv global 3.12.7
           
           # Create virtual environment with Python 3.12
           python3.12 -m venv /tmp/backend-venv