Add test workflow

Signed-off-by: Santiago Figueroa Manrique <figueroa1395@gmail.com>

Author: figueroa1395

.github/workflows/test-workflow.yml

@@ -0,0 +1,18 @@
+# SPDX-FileCopyrightText: Contributors to the Power Grid Model project <powergridmodel@lfenergy.org>
+#
+# SPDX-License-Identifier: MPL-2.0
+
+# This file works as a placeholder for new workflows to be tested
+# in the GitHub actions tab before being merged.
+# It is not intended to be used in the main branch, but rather in PRs.
+name: Test workflow
+
+on:
+  workflow_dispatch:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Test step
+        run: echo "Test workflow running"