fix: move test workflow to correct folder

.gitea/workflows/run-tests.yaml

@@ -0,0 +1,17 @@
+name: Run tests
+on:
+  push:
+
+jobs:
+  test-project:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out repository code
+        uses: actions/checkout@v4
+      - name: Install elixir
+        uses: erlef/setup-beam@v1
+      - name: Install dependencies
+        run: mix deps.get
+      - name: Run tests
+        run: mix test
+