Pull flake8 from Github

It seems flake8 is no longer available in Gitlab. This change switches
the source from Gitlab to Github to avoid the following failure.

fatal: could not read Username for 'https://gitlab.com': No such device
or address

(@matbu: moving podman CI job to non-voting to unblock this patch)

Closes-Bug: #1996668
Depends-on: https://review.opendev.org/c/openstack/tripleo-ci/+/864603
Change-Id: I5e50c0e9ffe2ab8cc527f2f2b4c887b09c5b1431

.pre-commit-config.yaml

@@ -22,7 +22,7 @@ repos:
         types: [file, yaml]
         entry: yamllint --strict -f parsable
 
-  - repo: https://gitlab.com/pycqa/flake8
+  - repo: https://github.com/pycqa/flake8
     rev: 3.9.1
     hooks:
       - id: flake8

.zuul.yaml

@@ -5,7 +5,7 @@
     run: playbooks/validations-libs-podified.yaml
     post-run: playbooks/post.yaml
     timeout: 7200
-    voting: true
+    voting: false
     required-projects:
       - openstack/validations-libs
       - openstack/validations-common
@@ -24,6 +24,7 @@
 
 - job:
     name: validations-libs-podified-docker
+    voting: true
     parent: validations-libs-podified-podman
     vars:
       container_engine: docker