chore: Update test-samples-impl.sh python3.6 --> python3.9 (#303)

Source-Link: googleapis/synthtool@1f07110 Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-python:latest@sha256:a5d81b61dfd1a432d3c03f51a25d2e71b37be24da509966d50724aea7c57c5c2 Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: gcf-owl-bot[bot]

.github/.OwlBot.lock.yaml

@@ -13,5 +13,5 @@
 # limitations under the License.
 docker:
  image: gcr.io/cloud-devrel-public-resources/owlbot-python:latest
- digest: sha256:b2dc5f80edcf5d4486c39068c9fa11f7f851d9568eea4dcba130f994ea9b5e97
-# created: 2022-06-12T16:09:31.61859086Z
+ digest: sha256:a5d81b61dfd1a432d3c03f51a25d2e71b37be24da509966d50724aea7c57c5c2
+# created: 2022-07-04T12:33:08.125873124Z

.kokoro/test-samples-impl.sh

@@ -33,7 +33,7 @@ export PYTHONUNBUFFERED=1
 env | grep KOKORO
 
 # Install nox
-python3.6 -m pip install --upgrade --quiet nox
+python3.9 -m pip install --upgrade --quiet nox
 
 # Use secrets acessor service account to get secrets
 if [[ -f "${KOKORO_GFILE_DIR}/secrets_viewer_service_account.json" ]]; then
@@ -76,7 +76,7 @@ for file in samples/**/requirements.txt; do
  echo "------------------------------------------------------------"
 
  # Use nox to execute the tests for the project.
- python3.6 -m nox -s "$RUN_TESTS_SESSION"
+ python3.9 -m nox -s "$RUN_TESTS_SESSION"
  EXIT=$?
 
  # If this is a periodic build, send the test log to the FlakyBot.