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.

pyproject.toml

@@ -8,7 +8,7 @@ version = "0.1.2"
 description = "NAPALM driver for TP-Link Jetstream managed switches"
 readme = "README.md"
 license = { text = "Apache-2.0" }
-requires-python = ">=3.8"
+requires-python = ">=3.10"
 authors = [
     { name = "Christian Manivong" },
 ]
@@ -16,8 +16,6 @@ classifiers = [
     "Topic :: Utilities",
     "License :: OSI Approved :: Apache Software License",
     "Programming Language :: Python :: 3",
-    "Programming Language :: Python :: 3.8",
-    "Programming Language :: Python :: 3.9",
     "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",