Update Linux CI scripts, more Python versions.

Update scripts to use actions/setup-python to install different Python
versions.  Add run-faber.sh and get-py-env.py scripts.  Add
test-ubuntu-py-ver.yml CI script to test with different Python versions.

.github/workflows/test-ubuntu-py2.yml

@@ -0,0 +1,58 @@
+name: Test Ubuntu, Python 2.x
+
+on:
+  push:
+  pull_request:
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    strategy:
+      fail-fast: false
+      matrix:
+        python: [python]
+        cxx: [g++]
+        std: [c++11]
+        include:
+          # Add the appropriate docker image for each compiler.
+          # The images from teeks99/boost-python-test already have boost::python
+          # pre-reqs installed, see:
+          # https://github.com/teeks99/boost-python-test-docker
+          - cxx: g++
+            docker-img: teeks99/boost-python-test:gcc-15_1.89.0
+
+    container:
+      image: ${{ matrix.docker-img }}
+
+    steps:
+    - uses: actions/checkout@v5
+
+    - name: setup prerequisites
+      run: |
+        # Warning: this is not necessarily the same Python version as the one configured above !
+        python3 -m pip install -U faber --break-system-packages
+    - name: build
+      run: |
+        ${{ matrix.python }} --version
+        ${{ matrix.cxx }} --version
+        faber -v
+        sed -e "s/\$PYTHON/${{ matrix.python }}/g" .ci/faber > ~/.faber
+        faber \
+          --with-boost-include=${BOOST_PY_DEPS} \
+          --builddir=build \
+          cxx.name=${{ matrix.cxx }} \
+          cxxflags=-std=${{ matrix.std }} \
+          cppflags=-std=${{ matrix.std }} \
+          -j`nproc`
+    - name: test
+      run: |
+        faber \
+          --with-boost-include=${BOOST_PY_DEPS} \
+          --builddir=build \
+          cxx.name=${{ matrix.cxx }} \
+          cxxflags=-std=${{ matrix.std }} \
+          cppflags=-std=${{ matrix.std }} \
+          -j`nproc` \
+          test.report

.github/workflows/test-ubuntu.yml

@@ -1,6 +1,10 @@
+# Test on Ubuntu with various compiler and language standard versions.
 name: Test Ubuntu
 
-on:  [push, pull_request]
+on:
+  push:
+  pull_request:
+  workflow_dispatch:
 
 jobs:
   build:
@@ -9,49 +13,37 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python: [python, python3]
+        python-version: ['3.14']
         cxx: [g++, clang++]
         std: [c++11, c++14, c++17]
         include:
-          # Add the appropriate docker image for each compiler.
-          # The images from teeks99/boost-python-test already have boost::python
-          # pre-reqs installed, see:
-          # https://github.com/teeks99/boost-python-test-docker
-          - cxx: clang++
-            docker-img: teeks99/boost-python-test:clang-21_1.89.0
-          - cxx: g++
-            docker-img: teeks99/boost-python-test:gcc-15_1.89.0
+          # Also test with free-threaded build of Python
+          - python-version: '3.14t'
+            cxx: clang++
+            std: c++17
 
     container:
-      image: ${{ matrix.docker-img }}
+      # Add the appropriate docker image for the compiler.
+      # The images from teeks99/boost-python-test already have boost::python
+      # pre-reqs installed, see:
+      # https://github.com/teeks99/boost-python-test-docker
+      image: ${{ matrix.cxx == 'g++' &&
+        'teeks99/boost-python-test:gcc-15_1.89.0' ||
+        'teeks99/boost-python-test:clang-21_1.89.0' }}
 
     steps:
     - uses: actions/checkout@v5
-
+    - name: setup python
+      uses: actions/setup-python@v5
+      with:
+        python-version: ${{ matrix.python-version }}
     - name: setup prerequisites
       run: |
-        # Warning: this is not necessarily the same Python version as the one configured above !
-        python3 -m pip install -U faber --break-system-packages
+        echo "CXX=${{ matrix.cxx }}" >> "$GITHUB_ENV"
+        echo "CXX_STD=${{ matrix.std }}" >> "$GITHUB_ENV"
     - name: build
       run: |
-        ${{ matrix.python }} --version
-        ${{ matrix.cxx }} --version
-        faber -v
-        sed -e "s/\$PYTHON/${{ matrix.python }}/g" .ci/faber > ~/.faber
-        faber \
-          --with-boost-include=${BOOST_PY_DEPS} \
-          --builddir=build \
-          cxx.name=${{ matrix.cxx }} \
-          cxxflags=-std=${{ matrix.std }} \
-          cppflags=-std=${{ matrix.std }} \
-          -j`nproc`
+        .github/run-faber.sh
     - name: test
       run: |
-        faber \
-          --with-boost-include=${BOOST_PY_DEPS} \
-          --builddir=build \
-          cxx.name=${{ matrix.cxx }} \
-          cxxflags=-std=${{ matrix.std }} \
-          cppflags=-std=${{ matrix.std }} \
-          -j`nproc` \
-          test.report
+        .github/run-faber.sh test.report