Fix test validators for Python 3

A couple of tests are failing with Python 3 because of a small problem in the Python code used for the test validators.

This MR fixes the tests in a backward (Python 2) compatible way.

added 1 deleted label

Thanks for taking care of this @clemenci!

• [2020-09-12 00:14] Validation started with lhcb-head-py3#1
• [2020-09-13 00:12] Validation started with lhcb-head-py3#2
• [2020-09-14 00:20] Validation started with lhcb-head-py3#3
• [2020-09-15 01:07] Validation started with lhcb-head-py3#4
• [2020-09-16 00:13] Validation started with lhcb-head-py3#5
• [2020-09-17 00:21] Validation started with lhcb-head-py3#6
• [2020-09-18 00:19] Validation started with lhcb-head-py3#7
• [2020-09-19 00:20] Validation started with lhcb-head-py3#8
• [2020-09-20 00:08] Validation started with lhcb-head-py3#9
• [2020-09-21 00:15] Validation started with lhcb-head-py3#10
• [2020-09-22 00:15] Validation started with lhcb-head-py3#11
• [2020-09-24 00:14] Validation started with lhcb-head-py3#12
• [2020-09-25 00:11] Validation started with lhcb-head-py3#13

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merged

mentioned in commit 5f8e7d8c

unassigned @dovombru

added testing label