[CI] Add CI tests that run only after a PR is merged to main

Currently used for testing pre-release versions of Cython

.github/workflows/post-merge-tests.yml

@@ -0,0 +1,48 @@
+name: Post-merge Tests
+on:
+  workflow_dispatch:  # allow manual triggering of this workflow
+    inputs:
+      outgoing_ref:
+        description: "The ref to be built. Can be a tag, commit hash, or branch name"
+        required: true
+        default: "main"
+  push:
+    # Run when the main branch is pushed to
+    branches:
+      - main
+
+jobs:
+  prerelease-cython:
+    name: Pre-release Cython
+    runs-on: ubuntu-22.04
+    timeout-minutes: 60
+    env:
+      HDF5_LIBDIR: /usr/lib/x86_64-linux-gnu/hdf5/serial
+      HDF5_INCLUDEDIR: /usr/include/hdf5/serial
+    steps:
+    - uses: actions/checkout@v3
+      name: Checkout the repository
+      with:
+        submodules: recursive
+    - name: Setup Python
+      uses: actions/setup-python@v4
+      with:
+        python-version: 3.11
+        architecture: x64
+    - name: Install Apt dependencies
+      run: |
+        sudo apt update
+        sudo apt install libboost-dev libopenblas-dev libhdf5-dev
+    - name: Upgrade pip
+      run: python3 -m pip install -U pip setuptools wheel
+    - name: Install Python dependencies
+      run: |
+        python3 -m pip install ruamel.yaml scons numpy pandas h5py pytest pytest-github-actions-annotate-failures
+        python3 -m pip install --pre cython
+    - name: Build Cantera
+      run: python3 `which scons` build env_vars=all
+        CXX=clang++-12 CC=clang-12 f90_interface=n extra_lib_dirs=/usr/lib/llvm/lib
+        -j2 debug=n --debug=time hdf_libdir=$HDF5_LIBDIR hdf_include=$HDF5_INCLUDEDIR
+    - name: Test Cantera
+      run:
+        python3 `which scons` test show_long_tests=yes verbose_tests=yes --debug=time