flatpak test action: trust git repo

Author: NikolasK-source

.github/workflows/flatpak_test.yml

@@ -13,6 +13,9 @@ jobs:
     steps:
     - uses: actions/checkout@v2
 
+    - name: Git config
+      run: git config --global --add safe.directory *
+
     - name: Init submodules
       run: git submodule init