fix: Join labels in issue workflow (#563)

Instead of merging #562, I think this should work to fix the problem.
Join the list with " " as the delimiter (because it's bash). This means
we can't have spaces in label names, but that seems to be a convention
we already use.

.github/workflows/issue.yml

@@ -18,7 +18,7 @@ jobs:
     - name: Parse the priority label into a Jira priority
       id: set_priority_var
       env:
-        LABELS: ${{ github.event.issue.labels.*.name }}
+        LABELS: ${{ join(github.event.issue.labels.*.name, ' ') }}
       run: |
         MY_RESULT=""
         for label in $LABELS