title: `git pull` fails with "Not possible to fast-forward" for existing history
body: <p>I've read a lot of other questions about the subject error message (&quot;Not possible to fast-forward&quot;) but none of them seem to apply to my situation.  I create a branch (<code>git checkout -b issue-215</code>), make a change, and commit locally.  I push the change, then make new changes and another local commit:</p>
  <pre><code>* 4b797d2a - (HEAD -&gt; issue-215) 
  * 180a7ab5 - (origin/issue-215)
  * 863ef01a - (origin/master, origin/HEAD, master)
  </code></pre>
  <p>ETA: as requested in a comment, the output of <code>git branch --all -v</code>:</p>
  <pre><code>* issue-215                 4b797d2a [ahead 1] 
    ... other branches ...
    master                    863ef01a 
    
    remotes/origin/issue-215  180a7ab5 
    ...other remotes....
    remotes/origin/HEAD       -&gt; origin/master
    remotes/origin/master     863ef01a 
  
  </code></pre>
  <p>There are no new remote changes, but VSCode wants to pull before it pushes.  That's where I get this error.  So, to troubleshoot, I run <code>git pull origin issue-215</code> manually, and get the following output:</p>
  <pre><code>$ git pull origin issue-215
  From ssh://my.repo/project
   * branch              issue-215  -&gt; FETCH_HEAD
  fatal: Not possible to fast-forward, aborting.
  </code></pre>
  <p>Keep in mind, there are no new changes on the server, and the history from my current local commit back to the branch on the remote, back to <code>master</code> and <code>origin/master</code>, is a straight line.  I am not trying to merge or rebase, my local code is already a direct child of the branch I'm supposed to be pulling.</p>
  <p>This only started happening about a month ago.  Previously, clicking the &quot;sync&quot; button in VSCode would work, but since then it always fails with this error message.  Could I have made some kind of gitconfig change that causes this behavior?  There's not much in my global gitconfig file, and it happens with at least 2 projects so I don't think it's something I did to the repository.</p>