Bump cloud debugger Python agent to version 2.13

PiperOrigin-RevId: 268037333
Change-Id: Ifa5be1fb3a0be1a07dd66a07927c58df68abd30e

Author: Louis Ye

src/googleclouddebugger/version.py

@@ -4,4 +4,4 @@
 # The major version should only change on breaking changes. Minor version
 # changes go between regular updates. Instances running debuggers with
 # different major versions will show up as two different debuggees.
-__version__ = '2.12'
+__version__ = '2.13'