add plenary install stage to ci test runner

.gitea/workflows/tests.yml

@@ -29,5 +29,13 @@ jobs:
       - name: Neovim Version
         run: nvim --version
 
+      - name: Install plenary.nvim
+        shell: bash
+        run: |
+          set -euo pipefail
+          target_dir="${HOME}/.local/share/nvim/site/pack/vendor/start/plenary.nvim"
+          mkdir -p "$(dirname "${target_dir}")"
+          git clone --depth 1 https://github.com/nvim-lua/plenary.nvim "${target_dir}"
+
       - name: Run Tests
         run: bash run_test.sh