linked-issue: read the description of a pull request into a milestone branch (#254) (#255)

GitHub links an issue from "Closes #N" only in a pull request into the
default branch. Into milestone/v0.3.8 or a wip/ branch the closing
references stay empty, so the check failed on every such pull request
however its description named the issue (#252 was the first). For a pull
request into another branch, the description is now read for the same
keywords GitHub accepts.


(cherry picked from commit 894c7f698f)

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

.github/workflows/pr-hygiene.yml

@@ -53,6 +53,9 @@ jobs:
                   REPO: ${{ github.repository }}
                   NUMBER: ${{ github.event.pull_request.number }}
                   LABELS: ${{ join(github.event.pull_request.labels.*.name, ',') }}
+                  BASE: ${{ github.event.pull_request.base.ref }}
+                  DEFAULT_BRANCH: ${{ github.event.repository.default_branch }}
+                  BODY: ${{ github.event.pull_request.body }}
               run: |
                   count=$(gh api graphql \
                       -f query='query($owner: String!, $name: String!, $number: Int!) {
@@ -68,6 +71,19 @@ jobs:
                       exit 0
                   fi
 
+                  # GitHub reads "Closes #N" only in a pull request into the
+                  # default branch, so one into `milestone/v0.3.8` or a `wip/`
+                  # branch links nothing that way and its closing references
+                  # stay empty, whatever the description says. There the
+                  # description is read here instead, with the keywords GitHub
+                  # itself accepts. The issue closes when the milestone's own
+                  # pull request reaches main and lists it (see #250).
+                  if [ "$BASE" != "$DEFAULT_BRANCH" ] \
+                      && printf '%s' "$BODY" | grep -Eiq '\b(close[sd]?|fix(e[sd])?|resolve[sd]?):? +#[0-9]+'; then
+                      echo "Into \`$BASE\`: names the issue it closes in its description." >> "$GITHUB_STEP_SUMMARY"
+                      exit 0
+                  fi
+
                   for exempt in bug chore dependencies deployment; do
                       case ",$LABELS," in
                           *",$exempt,"*)