[ci] Fix docs push (#12810)

This was missing a repo checkout and failing as in
https://ci.tlcpack.ai/blue/organizations/jenkins/tvm/detail/main/4302/pipeline.
This also adds in the changes from #12719:

Fixes #12600. The original solution there doesn't actually fix the
issue, there would need to be some job queue that could make sure to
reject old pushes. Since this case is pretty rare, generally the next
commit that comes along and builds will fix everything up so we can
ignore failures that happen on `push`es.

ci/jenkins/Deploy.groovy.j2

@@ -73,7 +73,7 @@ def deploy_docs() {
       script: '''
         cd tvm-site
         git remote add deploy https://$GITHUB_TOKEN:x-oauth-basic@github.com/apache/tvm-site.git
-        git push deploy $DOCS_DEPLOY_BRANCH
+        git push deploy $DOCS_DEPLOY_BRANCH || true
       ''',
       label: 'Upload docs to apache/tvm-site'
     )
@@ -90,6 +90,7 @@ def deploy() {
           feature_flag="env.DOCS_DEPLOY_ENABLED == 'yes'",
           ws="tvm/deploy-docs",
         ) %}
+          init_git()
           {{ m.download_artifacts(tag='docs', filenames=["docs.tgz"]) }}
           deploy_docs()
         {% endcall %}