Bug 1712998 - Convert telemetry unittests to use Python 3 in CI, r=chutten

Differential Revision: https://phabricator.services.mozilla.com/D116035

taskcluster/ci/source-test/python.yml

@@ -525,7 +525,7 @@ telemetry-python:
         - linux1804-64/opt
         - macosx1014-64/opt
         - windows10-64/opt
-    python-version: [2]
+    python-version: [3]
     treeherder:
         symbol: tp
     run:

toolkit/components/telemetry/tests/python/python.ini

@@ -1,5 +1,4 @@
 [DEFAULT]
-skip-if = python == 3
 subsuite = telemetry-python
 
 [test_gen_event_data_json.py]

toolkit/components/telemetry/tests/python/test_gen_event_data_json.py

@@ -8,7 +8,7 @@ import os
 import sys
 import tempfile
 import unittest
-from StringIO import StringIO
+from io import StringIO
 from os import path
 
 TELEMETRY_ROOT_PATH = path.abspath(
@@ -26,7 +26,7 @@ class TestEventDataJson(unittest.TestCase):
     maxDiff = None
 
     def test_JSON_definitions_generation(self):
-        EVENTS_YAML = """
+        EVENTS_YAML = b"""
 with.optout:
   testme1:
     objects: ["test1"]

toolkit/components/telemetry/tests/python/test_gen_scalar_data_json.py

@@ -8,7 +8,7 @@ import os
 import sys
 import tempfile
 import unittest
-from StringIO import StringIO
+from io import StringIO
 from os import path
 
 TELEMETRY_ROOT_PATH = path.abspath(
@@ -25,7 +25,7 @@ class TestScalarDataJson(unittest.TestCase):
     maxDiff = None
 
     def test_JSON_definitions_generation(self):
-        SCALARS_YAML = """
+        SCALARS_YAML = b"""
 newscalar:
   withoptin:
     bug_numbers: