Add temp upterm debug step

Author: JustinGrote

.github/workflows/vim-test.yml

@@ -59,6 +59,9 @@ jobs:
           repository: thinca/vim-themis
           path: vim-themis
 
+      - name: Debug if run with debugging enabled
+        uses: lhotari/action-upterm@v1
+
       - name: Run Themis with full CLI
         env:
           THEMIS_VIM: ${{ steps.vim.outputs.executable }}