.gitlab-ci.yml: Run python3.8 and 3.9 tests with coverage

Now that we are using a threaded scheduler, coverage works with
python3.8 and python3.9

.gitlab-ci.yml

diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 2031e27..b78b7ea 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -30,7 +30,7 @@
   INTEGRATION_CACHE: "${CI_PROJECT_DIR}/cache/integration-cache"
   PYTEST_ARGS: "--color=yes --integration -n 2"
   TEST_COMMAND: "tox -- ${PYTEST_ARGS}"
-  TOXENV: py36, py37, py38-nocover, py39-nocover, py36-plugins, py37-plugins, py38-plugins-nocover, py39-plugins-nocover
+  TOXENV: py36, py37, py38, py39, py36-plugins, py37-plugins, py38-plugins, py39-plugins
   COVERAGE_PREFIX: "${CI_JOB_NAME}."
 
 
@@ -364,7 +364,7 @@
   - chown -R buildstream:buildstream .
 
   # Don't run tests multiprocessed here, the randomized order doesn't like that
-  - su buildstream -c "tox -e py36-randomized,py37-randomized,py38-randomized-nocover -- --color=yes --integration"
+  - su buildstream -c "tox -e py36-randomized,py37-randomized,py38-randomized,py39-randomized -- --color=yes --integration"
 
   # We need to override the exclusion from the template in order to run on schedules
   except: []

tox.ini

diff --git a/tox.ini b/tox.ini
index c06d17b..a50f594 100644
--- a/tox.ini
+++ b/tox.ini
@@ -2,7 +2,7 @@
 # Tox global configuration
 #
 [tox]
-envlist = py{36,37},py38-nocover,py39-nocover
+envlist = py{36,37,38,39}
 skip_missing_interpreters = true
 isolated_build = true