Update Zuul CI

* Flake8 is moved to github now.
* tox-py38 job is broken on opendev - it uses default nodeset, which
  runs on ubuntu-jammy. But ubuntu-jammy does not have python 3.8,
  and job fails.
  Override it's nodeset to ubuntu-focal, which still has it.

Change-Id: Id9b20f48f112f659bbb4e891e73933b1c56250c1

.pre-commit-config.yaml

@@ -12,7 +12,7 @@ repos:
       - id: check-added-large-files
       - id: end-of-file-fixer
       - id: trailing-whitespace
-  - repo: https://gitlab.com/pycqa/flake8.git
+  - repo: https://github.com/PyCQA/flake8
     rev: 3.7.8
     hooks:
       - id: flake8

.zuul.yaml

@@ -11,6 +11,7 @@
     required-projects:
       - jjb/python-jenkins
       - jjb/jenkins-job-builder
+    nodeset: ubuntu-focal
     voting: true
 
 - job:
@@ -23,12 +24,17 @@
     templates:
       - docs-on-readthedocs
       - openstack-python37-jobs-no-constraints
-      - openstack-python38-jobs-no-constraints
     vars:
       rtd_webhook_id: '47271'
     check:
       jobs:
+        - tox-py38:
+            nodeset: ubuntu-focal
         - jjb-tox-linters
         - jjb-tox-cross-python-jenkins
         - jjb-tox-docs-linkcheck
         - tox-cover
+    gate:
+      jobs:
+        - tox-py38:
+            nodeset: ubuntu-focal