git backup a remote repository with another remote

I have a remote repository on github and another remote repository for backup. Since the repository is very big I don't want everytime to use git push --mirror (it is above 20GB) and want to sync only latest changes everytime.

I want to write a script that is doing something like this:

for each branch in githubRemote/branches do:
  if branch != otherRemote/branch:
     checkout githubRemote/branch
     push branch to otherRemote

based on @Levi Lu-MSFT's answer, I wrote this script:

git checkout master
git reset --hard

$branches = git branch -r  | foreach{ $_ -replace "^.*?\/", "" } | where {$_ -notmatch "HEAD" }
 
foreach($branch in $branches)
{
   
    $branchBackupHash = git rev-parse remoteTFS/$branch
    $branchWorkingHash = git rev-parse remoteGithub/$branch
    #check if the commit hash is the same
    if($branchBackupHash -ne $branchWorkingHash)
    {
      echo updating branch $branch
      git checkout origin/$branch -q
      git pull origin $branch
      git push remoteTFS $branch
    }
 }