Drop Python 2.6 support and add 3.7
PIP requires Python 2.7, so it is not possible to test using anything prior to that.
Python 3.7 has been out for a while, so we can test against it.
GitLab Registry scheduled maintenance on Wednesday, October 09th 2024 as of 20:00h Geneva time for a period of 1 hour. Further information under https://cern.ch/otg0152540.
PIP requires Python 2.7, so it is not possible to test using anything prior to that.
Python 3.7 has been out for a while, so we can test against it.