fix(ci): create empty .gitmodules before submodule add in sync-releases

The previous fix (87163ba) removed the explicit `printf > .gitmodules`
line, assuming `git submodule add` would create the file on its own.
It doesn't when the parent step already wiped the working tree —
submodule add refuses with:
  fatal: please make sure that the .gitmodules file is in the working tree

Create an empty .gitmodules (and stage it) before the add call.

Author: DavidsonGomes

.github/workflows/sync-releases.yml

@@ -117,6 +117,8 @@ jobs:
           cd ${{ steps.target.outputs.dir }}
           git rm -rf whatsmeow-lib 2>/dev/null || true
           rm -rf whatsmeow-lib .gitmodules
+          : > .gitmodules
+          git add .gitmodules
           git submodule add -f https://github.com/EvolutionAPI/whatsmeow.git whatsmeow-lib
           cd whatsmeow-lib
           git checkout "$WHATSMEOW_SHA"