Handle reusing a pull request

We were hitting an error where gh pr create would fail when a PR already
existed for a branch. This is unfortunately not an easy case to handle,
as the tool isn't very smart. See:

    cli/cli#5792

To work-around that limitation, we first try to edit the PR. If that
fails, we create a new PR. However, I've noticed edit will succeed for
closed PRs (which makes sense), so we try to reopen after edit, which
succeeds if the PR is already open.

This is not working 100% as intended, as gh pr reopen currently fails
to actually reopen closed PRs. The end result is reasonable, though, as
we get a newly created PR when the previous one was closed.

.github/workflows/ci.yml

@@ -87,7 +87,7 @@ jobs:
         if: env.DID_IMPORT == '1'
         run: |
           echo ${{ secrets.GH_TOKEN }} | gh auth login --with-token
-          gh pr create --fill -B main -H ${{ env.BRANCH_NAME }}
+          gh pr edit ${{ env.BRANCH_NAME }} -b '${{ env.PR_BODY }}' -t '${{ env.PR_TITLE }}'  && gh pr reopen ${{ env.BRANCH_NAME }} || gh pr create --fill -B main -H ${{ env.BRANCH_NAME }}
 
       - name: Upload PDFs
         if: env.DID_IMPORT == '1'