Add a pre-check job to bootstrap the environment on Python 3.6 (#36358)

* Add a pre-check job that just bootstrap the environment on Python 3.6
* py-typing-extension: restore information on Python 3.6 installation
* Fix job name, try to run quick test on installed python packages

.github/workflows/valid-style.yml

@@ -58,3 +58,28 @@ jobs:
     with:
       with_coverage: ${{ inputs.with_coverage }}
       python_version: '3.11'
+  # Check that spack can bootstrap the development environment on Python 3.6 - RHEL8
+  bootstrap-dev-rhel8:
+    runs-on: ubuntu-latest
+    container: registry.access.redhat.com/ubi8/ubi
+    steps:
+      - name: Install dependencies
+        run: |
+          dnf install -y \
+              bzip2 curl file gcc-c++ gcc gcc-gfortran git gnupg2 gzip \
+              make patch tcl unzip which xz
+      - uses: actions/checkout@24cb9080177205b6e8c946b17badbe402adc938f # @v2
+      - name: Setup repo and non-root user
+        run: |
+          git --version
+          git fetch --unshallow
+          . .github/workflows/setup_git.sh
+          useradd spack-test
+          chown -R spack-test .
+      - name: Bootstrap Spack development environment
+        shell: runuser -u spack-test -- bash {0}
+        run: |
+          source share/spack/setup-env.sh
+          spack -d bootstrap now --dev
+          spack style -t black
+          spack unit-test -V

var/spack/repos/builtin/packages/py-typing-extensions/package.py

@@ -26,5 +26,8 @@ class PyTypingExtensions(PythonPackage):
     version("3.7.2", sha256="fb2cd053238d33a8ec939190f30cfd736c00653a85a2919415cecf7dc3d9da71")
     version("3.6.6", sha256="51e7b7f3dcabf9ad22eed61490f3b8d23d9922af400fe6656cb08e66656b701f")
 
+    # typing-extensions 4+ uses flit
+    depends_on("python@3.7:", when="@4.2:", type=("build", "run"))
+    depends_on("python@3.6:", when="@4:", type=("build", "run"))
     depends_on("py-flit-core@3.4:3", when="@4:", type="build")
     depends_on("py-setuptools", when="@:3", type="build")