Fix upload-db-dump action script

It just failed:

    Run git checkout db-dumps
    error: Your local changes to the following files would be overwritten by checkout:
	    util/dev-config/config.toml
    Please commit your changes or stash them before you switch branches.

Well, I still haven't tested this, so we will see during the next
release :P

.github/workflows/upload-db-dump.yml

@@ -72,6 +72,7 @@ jobs:
       # the dump is 2MB, this "waste" of storage and bandwidth is miniscule.
       - name: Commit & push
         run: |
+          git reset --hard HEAD
           git checkout db-dumps
           cp db-dump.xz db-dump-latest.xz
           mv db-dump.xz db-dump-${{github.ref_name}}.xz