ci: Force Python 3.10 for testing

Python 3.10 is currently the minimum Python version supported by Zephyr
and the version intended to be used with Zephyr SDK (note that `gdb-py`
links against `libpython3.10`), so test with Python 3.10 on all host
operating sytems.

As part of this, virtual environment usage is forced on Linux hosts in
order to ensure that the correct version and installation of Python is
used.

Signed-off-by: Stephanos Ioannidis <[email protected]>

.github/workflows/ci.yml

@@ -1429,11 +1429,10 @@ jobs:
 
     steps:
     - name: Set up Python
-      if: ${{ runner.os == 'Windows' }}
       uses: actions/setup-python@v5
       with:
-        # Force Python 3.10 because the twister is not compatible with a Python
-        # version lower than 3.8 on Windows.
+        # Force Python 3.10, which is the minimum Python version supported by
+        # Zephyr and intended to be used with Zephyr SDK.
         python-version: '3.10'
 
     - name: Set up test environment (Linux)
@@ -1467,7 +1466,6 @@ jobs:
         echo "ARTIFACT_ROOT=${GITHUB_WORKSPACE}/artifacts" >> $GITHUB_ENV
 
     - name: Create Python virtual environment
-      if: ${{ runner.os != 'Linux' }}
       run: |
         # Create Python virtual environment
         python3 -m venv ${GITHUB_WORKSPACE}/venv
@@ -1568,19 +1566,15 @@ jobs:
     - name: Install west
       run: |
         # Activate Python virtual environment
-        if [ ! -z "${VENV_ACTIVATE}" ]; then
-          source ${VENV_ACTIVATE}
-        fi
+        source ${VENV_ACTIVATE}
 
         # Install or upgrade west
         pip3 install --upgrade west
 
     - name: Set up Zephyr repository
       run: |
         # Activate Python virtual environment
-        if [ ! -z "${VENV_ACTIVATE}" ]; then
-          source ${VENV_ACTIVATE}
-        fi
+        source ${VENV_ACTIVATE}
 
         # Create Zephyr workspace
         ZEPHYR_WORKSPACE=${GITHUB_WORKSPACE}/zephyrproject
@@ -1610,21 +1604,15 @@ jobs:
     - name: Install Python dependencies
       run: |
         # Activate Python virtual environment
-        if [ ! -z "${VENV_ACTIVATE}" ]; then
-          source ${VENV_ACTIVATE}
+        source ${VENV_ACTIVATE}
 
-          # Install Python dependencies from the checked out Zephyr repository
-          # if running inside a virtual environment; otherwise, it is assumed
-          # that the host already provides all the required dependencies.
-          pip3 install -r ${ZEPHYR_ROOT}/scripts/requirements.txt
-        fi
+        # Install Python dependencies from the checked out Zephyr repository.
+        pip3 install -r ${ZEPHYR_ROOT}/scripts/requirements.txt
 
     - name: Run test suites
       run: |
         # Activate Python virtual environment
-        if [ ! -z "${VENV_ACTIVATE}" ]; then
-          source ${VENV_ACTIVATE}
-        fi
+        source ${VENV_ACTIVATE}
 
         # Create working directory
         mkdir -p test