chore: update Jenkinsfile with the new base

I've force-pushed the `.asf.yaml` change to the `asf-site` branch, and
that means that there is now a new base to squash against. Also this
adds a `grep -v` to remove the `create mode 100644` messages from git
that the `-q` doesn't silence.
diff --git a/Jenkinsfile b/Jenkinsfile
index 175dc60..bed37b2 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -17,6 +17,7 @@
  * under the License.
  */
 def NODE = 'git-websites'
+def STOP_SQUASH_AT = '5570b6e2e57afb5f0a8f78f9bf9c33bd6f16aaed'
 
 pipeline {
     agent {
@@ -87,7 +88,7 @@
                 dir('deploy/staging') {
                     deleteDir()
                     sh 'git clone -b asf-site https://gitbox.apache.org/repos/asf/camel-website.git .'
-                    sh 'git -c core.editor="sed -i 2,/$(git log --skip=9 -1 --pretty=format:%h)/s/^pick/squash/" rebase -q --interactive 1586f65bf7f24784dc99e22aff08e44c7dbb1920' // squash all but initial and last 9 commits
+                    sh "git -c core.editor='sed -i 2,/\$(git log --skip=9 -1 --pretty=format:%h)/s/^pick/squash/' rebase -q --interactive $STOP_SQUASH_AT | grep -v 'create mode 100644'" // squash all but initial and last 9 commits
                     sh 'git rm -q -r *'
                     sh "cp -R $WORKSPACE/camel-website/public/. ."
                     sh 'git add .'