Set pseudo committer info

Author: tautschnig

.github/workflows/update-subtree.yml

@@ -78,7 +78,7 @@ jobs:
           echo "Nothing to cherry-pick, ${UPSTREAM_FROM} matches ${UPSTREAM_HEAD} (${SUBTREE_HEAD_MSG})"
           echo "MERGE_CONFLICTS=noop" >> $GITHUB_ENV
         else
-          git cherry-pick ${UPSTREAM_FROM}..rust-filtered/subtree/library
+          git -c user.name=gitbot -c user.email=git@bot cherry-pick ${UPSTREAM_FROM}..rust-filtered/subtree/library
           echo "MERGE_CONFLICTS=maybe" >> $GITHUB_ENV
         fi