fix: issue templates used outdated label names (#2991)

.github/ISSUE_TEMPLATE/2-web-bug.yml

@@ -1,6 +1,6 @@
 name: 🌐 Website bug (modrinth.com)
 description: Report an issue on the Modrinth website.
-labels: [bug, frontend]
+labels: [bug, web]
 body:
   - type: checkboxes
     attributes:

.github/ISSUE_TEMPLATE/3-api-bug.yml

@@ -1,6 +1,6 @@
 name: 🛠️ API issue (api.modrinth.com)
 description: Report an issue regarding the Modrinth API.
-labels: [bug, api]
+labels: [bug, backend]
 body:
   - type: checkboxes
     attributes: