chore(deps): update dependency pytest to v6.2.4 (#328)

Author: renovate-bot

packages/google-cloud-spanner/samples/samples/requirements-test.txt

@@ -1,3 +1,3 @@
-pytest==6.0.1
+pytest==6.2.4
 mock==4.0.2
 google-cloud-testutils==0.1.0