skip prerelease_deps for 3.7 and 3.8

Author: ohmayr

packages/google-cloud-pubsub/noxfile.py

@@ -457,6 +457,9 @@ def docfx(session):
 def prerelease_deps(session, protobuf_implementation):
     """Run all tests with prerelease versions of dependencies installed."""
 
+    if session.python in ["3.7", "3.8"]:
+        session.skip(f"Python {session.python} is no longer supported.")
+
     if protobuf_implementation == "cpp" and session.python in (
         "3.11",
         "3.12",