[ci] Ignore empty nightly docs commits instead of failing

.github/workflows/nightly_docs.yml

@@ -59,5 +59,8 @@ jobs:
           path: ./static/docs-rs/bdk/nightly/latest
       - name: Configure git
         run: git config user.email "github-actions@github.com" && git config user.name "github-actions"
-      - name: Commit and push
-        run: git add ./static && git commit -m "Publish autogenerated nightly docs" && git push origin master
+      - name: Commit
+        continue-on-error: true         # If there's nothing to commit this step fails, but it's fine
+        run: git add ./static && git commit -m "Publish autogenerated nightly docs"
+      - name: Push
+        run: git push origin master