ci(digest): close existing open digest PRs before creating new one (#42)

Problem: if a digest PR is not merged before the next weekly run, a
second PR is created for the same items plus any new ones, leading
to duplicate open PRs.

Solution: before fetching upstream activity, close any open PRs
labeled upstream/digest (deleting their branches). The new run
re-fetches all items since the last merged baseline and produces a
single up-to-date PR.

.github/workflows/upstream-digest.yml

@@ -15,6 +15,20 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      - name: Close existing digest PRs
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          gh pr list \
+            --repo barrettruth/canola.nvim \
+            --label "upstream/digest" \
+            --state open \
+            --json number \
+            --jq '.[].number' \
+          | xargs -r -I{} gh pr close {} \
+              --repo barrettruth/canola.nvim \
+              --delete-branch
+
       - name: Update upstream tracker
         id: digest
         env:
@@ -42,5 +56,6 @@ jobs:
             --title "docs(upstream): add digest for week of ${DATE}" \
             --body "Automated weekly digest of new upstream activity. Triage by updating statuses and notes." \
             --base main \
-            --head "${BRANCH}")
+            --head "${BRANCH}" \
+            --label "upstream/digest")
           gh pr merge "${PR_URL}" --auto --squash