Backport PR #936 on branch 2.4 (Fix subpackage update workflow for 2.4) (#937)

Co-authored-by: Stuart Mumford <stuart@cadair.com>

Author: meeseeksmachine

.github/workflows/sub_package_update.yml

@@ -88,7 +88,7 @@ jobs:
           title: "Updates from the package template"
           labels: |
             No Changelog Entry Needed
-            Backport 2.3
+            Backport 2.4
           body: |
             This is an autogenerated PR, which will applies the latest changes from the [SunPy Package Template](https://github.com/sunpy/package-template).
             If this pull request has been opened as a draft there are conflicts which need fixing.