fix(github): point the issue templates at labels that exist (#43357)

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

.github/ISSUE_TEMPLATE/bug-report.yml

@@ -1,6 +1,6 @@
 name: Bug report
 description: Report a bug to improve Superset's stability
-labels: ["bug"]
+labels: ["#bug"]
 body:
   - type: markdown
     attributes:

.github/ISSUE_TEMPLATE/cosmetic.md

@@ -1,7 +1,7 @@
 ---
 name: Cosmetic Issue
 about: Describe a cosmetic issue with CSS, positioning, layout, labeling, or similar
-labels: "cosmetic-issue"
+labels: "#bug:cosmetic"
 ---
 
 ## Screenshot