Push to fork before checking for existing PR

Previously, when doing propose downstream, we checked for
an already existing PR, and only if there was none, we pushed changes
to a fork and created a new PR.
Initially, the checking for already existing PR had been added in packit#994
in order to prevent creating multiple PRs if more propose-downstream
jobs are triggered (packit/packit-service#785).

This prevents us from updating an already existing PR (packit/hardly#76),
so with this change, we first push to a fork,
which might update an already existing PR,
and then we check whether we actually need to create a new PR
or if there already is one.

packit/api.py

@@ -1069,10 +1069,11 @@ def push_and_create_pr(
         git_branch: str,
         repo: Union[Upstream, DistGit],
     ) -> PullRequest:
+        # the branch may already be up, let's push forcefully
+        repo.push_to_fork(repo.local_project.ref, force=True)
+
         pr = repo.existing_pr(pr_title, pr_description.rstrip(), git_branch)
         if pr is None:
-            # the branch may already be up, let's push forcefully
-            repo.push_to_fork(repo.local_project.ref, force=True)
             pr = repo.create_pull(
                 pr_title,
                 pr_description,