telink: Fix for coding_guidelines CI (zephyrproject-rtos#34)

Fix CI configuration for checking coding guidelines.

Signed-off-by: Maciej Bojczuk <maciej.bojczuk@telink-semi.com>

Author: Maciej Bojczuk

.github/workflows/coding_guidelines.yml

@@ -4,7 +4,7 @@ on: pull_request
 
 jobs:
   compliance_job:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     name: Run coding guidelines checks on patch series (PR)
     steps:
     - name: Checkout the code