As of ibm-vpc 0.28.0, a version parameter is required. [1]
The old default value for the version was "2025-03-04", but the
documentation states that the min value is now "2025-04-08". Setting
this min value as the version to try and be compatible to the previous
value.
This fixes failing tests for the ibmvpc driver.
[1] https://github.com/IBM/vpc-python-sdk/pull/88
Change-Id: I351af87d8e47e71c2d5dd2ef0820e430e1f5b9ee