revert: remove concurrency from gha

The `cancel-in-progress` option for concurrency is not really supported by Gitea, so the whole point of the block no longer makes any sense.

.gitea/workflows/ci.yml

@@ -1,9 +1,5 @@
 name: CI TEST3
 
-concurrency:
-  group: ${{ github.workflow }}-${{ github.ref }}
-  cancel-in-progress: true
-
 on:
   push:
     branches: [main]