add linting check and fix warning

There is this linting message:
```
[208] File permissions unset or incorrect
tasks/main.yml:27
Task/Handler: Create config and data directory
```

I fixed it in this commit and added a github action
to run the official™ ansible linting check!

.github/workflows/ansible-linting-check.yml

@@ -0,0 +1,20 @@
+name: Ansible Lint check
+
+on: [push, pull_request]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: Lint Ansible Playbook
+      uses: ansible/ansible-lint-action@master
+      with:
+        targets: "."
+        # [required]
+        # Paths to ansible files (i.e., playbooks, tasks, handlers etc..)
+        args: ""
+        # [optional]

tasks/main.yml

@@ -29,6 +29,7 @@
     path: "{{ item }}"
     state: directory
     owner: "{{ gitea_user }}"
+    mode: '0755'
     recurse: True
   with_items:
     - "/etc/gitea"