Fixed lit install on ARCH Linux - venv instead of system install

Step 5/10 : RUN pip3 install lit
 ---> Running in 2e06fb37c145
error: externally-managed-environment

× This environment is externally managed
╰─> To install Python packages system-wide, try 'pacman -S
    python-xyz', where xyz is the package you are trying to
    install.

    If you wish to install a non-Arch-packaged Python package,
    create a virtual environment using 'python -m venv path/to/venv'.
    Then use path/to/venv/bin/python and path/to/venv/bin/pip.

    If you wish to install a non-Arch packaged Python application,
    it may be easiest to use 'pipx install xyz', which will manage a
    virtual environment for you. Make sure you have python-pipx
    installed via pacman.

note: If you believe this is a mistake, please contact your Python installation or OS distribution provider. You can override this, at the risk of breaking your Python installation or OS, by passing --break-system-packages.
hint: See PEP 668 for the detailed specification.

Dockerfile_archlinux

@@ -14,6 +14,7 @@ FROM archlinux
 
 ENV LLVM_DIR /usr/
 ENV TUTOR_DIR /llvm-tutor
+ENV VENV_DIR /venv
 
 # 1. INSTALL DEPENDENCIES
 RUN pacman -Syu --noconfirm \
@@ -26,7 +27,9 @@ RUN pacman -Syu --noconfirm \
     python-pip
 
 # 2. INSTALL LIT
-RUN pip3 install lit
+RUN python3 -m venv $VENV_DIR
+RUN source ./env/bin/activate
+RUN pip install lit
 
 # 3. CLONE LLVM-TUTOR
 RUN git clone https://github.com/banach-space/llvm-tutor $TUTOR_DIR
@@ -44,4 +47,4 @@ RUN mkdir -p $TUTOR_DIR/build \
     && cd $TUTOR_DIR/build \
     && cmake -G Ninja -DLT_LLVM_INSTALL_DIR=$LLVM_DIR ../ \
     && ninja \
-    && lit test/
+    && $VENV_DIR/bin/lit test/