ci: install napalm-device-types from git, so the tests run at all

Every CI run died at "pip install -e .[dev]": pyproject.toml asks for
napalm_device_types, which lives in git.netork.io/NAPALM rather than on PyPI,
and pip found only an unrelated 0.1.0 there. Not one test had run in CI.

The workflow now installs napalm-device-types from git first. The matrix
drops 3.8/3.9 and requires-python says >=3.10, because napalm-device-types
itself needs 3.10 -- the package never installed on anything older.

Replayed in a fresh venv: napalm-device-types 2.0.0 from git, then the
package with its dev extras, tests green.

.github/workflows/tests.yml

@@ -13,7 +13,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12"]
+        python-version: ["3.10", "3.11", "3.12"]
 
     steps:
       - uses: actions/checkout@v4
@@ -25,6 +25,9 @@ jobs:
 
       - name: Install dependencies
         run: |
+          # napalm-device-types lives in git.netork.io/NAPALM, not on PyPI: without this
+          # pip looks there, finds an unrelated 0.1.0 and the job dies before any test.
+          pip install "napalm-device-types @ git+https://git.netork.io/NAPALM/napalm-device-types.git"
           pip install -e ".[dev]"
 
       - name: Run tests