title: git fetch only into specified target branch
body: <p>I'm writing a test script for a CI/CD system and need to checkout the source and target branches of a pull request and do some verifications.<br />
  I would like to have fixed branch names in my local repo (<code>src</code> and <code>target</code>) and hence I use refspecs with a target branch for my fetches.
  But additionally to my target branch git also fetches into a target branch with the original name of that branch (marked bold below). In the git fetch manpage I didn't even find a hint that git should behave this way.
  This issue leads sometimes to name conflicts and I want to avoid that.</p>
  <pre><code>
  + git fetch --no-tags -f origin feature/some-feature:refs/remotes/origin/src
  From github.com:user/repo
   * [new branch]        feature/some-feature -> origin/src
  <b> * [new branch]        feature/some-feature -> origin/feature/some-feature</b>
   
  + git fetch --no-tags -f origin master:refs/remotes/origin/target
  From github.com:user/repo
   * [new branch]        master    -> origin/target
  <b> * [new branch]        master    -> origin/master</b>
  </code></pre>
  <p>How can I make git stop fetching into branches with original names from remote and use only the target branch names I explicitly mention (how to remove bold lines)?</p>