dotnet-bump: allow running manually

Signed-off-by: Ilya Leoshkevich <[email protected]>

Author: iii-i

.github/workflows/bump.yml

@@ -1,6 +1,7 @@
 on:
   schedule:
   - cron: '0 0 * * *'
+  workflow_dispatch:
 
 permissions:
   contents: write