fix(gapic-generator): remove lagging 3.9 refs (#16924)

> [!note]
> This PR was in a holding pattern. It should be merged now that we have
removed the references to 3.9 in the repo (via generation of the GAPIC
libraries and via updates to the handwritten libs)

Removes two lagging refs to 3.9 to finalize the migration of the gapic
generator codebase to 3.10+ runtime dependencies.

Fixes #[internal issue](http://b/482126936) 🦕

Author: chalmerlowe

.github/workflows/unittest.yml

@@ -18,7 +18,7 @@ jobs:
     strategy:
       fail-fast: true
       matrix:
-        python: ['3.9', '3.10', "3.11", "3.12", "3.13", "3.14"]
+        python: ['3.10', "3.11", "3.12", "3.13", "3.14"]
     steps:
     - name: Checkout
       uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6

ci/run_single_test.sh

@@ -70,15 +70,6 @@ case ${TEST_TYPE} in
         ;;
     unit)
         case ${PY_VERSION} in
-        "3.9")
-            if nox --list-sessions | grep -q "unit-3.9"; then
-                nox -s unit-3.9
-                retval=$?
-            else
-                echo "Skipping unit-3.9 as it is not supported by this package."
-                retval=0
-            fi
-            ;;
         "3.10")
             nox -s unit-3.10
             retval=$?

packages/gapic-generator/noxfile.py

@@ -44,7 +44,6 @@
 RUFF_EXCLUDES = "*golden*,*pb2.py,*pb2.pyi"
 
 ALL_PYTHON = (
-    "3.9",
     "3.10",
     "3.11",
     "3.12",
@@ -59,8 +58,7 @@
 @nox.session(python=ALL_PYTHON)
 def unit(session):
     """Run the unit test suite."""
-    if session.python == "3.9":
-        session.skip("Skipping Python 3.9 unit tests temporarily.")
+
     session.install(
         # TODO(https://github.com/googleapis/gapic-generator-python/issues/2478):
         # Temporarily pin coverage to 7.11.0