Update submodule-update.yml

allow manual runs with workflow_dispatch

.github/workflows/submodule-update.yml

@@ -1,6 +1,8 @@
 name: Send submodule updates to joshuah345.github.io
 
 on:
+  workflow_dispatch:
+
   push:
     branches: 
       - main
@@ -27,4 +29,4 @@ jobs:
           git config user.name "GitHub Actions - update submodules"
           git add --all
           git commit -m "Update submodules" || echo "No changes to commit"
-          git push
+          git push